i can get to the high notes, but the notes sound pinched and screechy, it's also hard to stay on the high note for example, high high F, i can get there, but then after a while i lose the note and go down an octave against my will, any tips?

Just keep practicing your high range. Also, practice your low low range too. Pedal tones all the way! Practice the low notes will actually help your high range, and you'll also developed a greater range as a whole with better tone all around.

Practice practice practice!

It takes time to develop the lip muscles - so dont expect too much. You should aim to use little or no pressure and think about the shape of the opening in the lips (a narrow slit is one possible cause of a poor tone which would disappear if you had the lip muscles to maintain an oval - oboe reed - opening). According to Phillip Farkas "The Art of French Horn Playing" you should achieve lip tension without stretching the lips or using pressure.

Once you are happy that your technique is correct then gradually increase the range you practice over a period of weeks!

<Added>

How high is a high high F? F written on the top of the treble clef stave?

If your going after the octive above, then you probably should be using a descant horn.

i refer to high high f as the f above the top note on the staff, you know, the top note on the two octave concert c scale? yeah, that one.

If you're concerned about playing F above top C (ie written above the 3rd ledger line - 3 octaves above the F fundamental on the Bb side) then my advice is don't bother. IMHO, its never a nice note and only ever written by composers/arrangers who should (and often do) know better. The reason they don't include a flugel horn player in the score is sometimes because they dont have the experience to know that instrument would sound better (more horn-like) playing that note and can do so with much more reliability than even on a F descant horn. (In extreme cases its just that the composer/arranger has an irrational bias towards regular orchestral instruments). In other words, playing that high is a technical challenge which is unlikely to be important even in professional horn playing.

Inadvertently, dropping an octave is strange and is unlikely to be something simple like insufficient breath support. It may reflect using a different embouchure for such notes which your lip muscles simply cant hold. Do you suffer from lip fatique on high notes (C in the stave to top C) towards the end of long playing sessions?

What are pedal tones????
And how can you NOT use pressure?

I must be doing it very wrong...

pedal tones are the notes you can go down to if you fit a low f sharp and try to go lower, you cant hit the f right, but you can hit a C below it

not using pressure involves avoiding the deep red mark u get on your face after you play for a while or try to play a high note

You can stretch your lips like an elastic band to increase their tension. This makes them thinner and more easily damaged by pressure which is the intuitive way of supporting the lip stretching. To play higher notes, lips have to vibrate faster which will only happen when they are more tense. When you whistle you also tense lip muscles but in a way which does not make them thinner. The Phillip Farkas "puckered smile" embouchure is worth reading about. It achieves lip tension without stretching and consequently give good endurance - especially to players with larger lips who have no choice but to set the mouthpiece rim into the lower or both lips.

Using pressure was popular in the first have of last century across most brass instruments and some of the extra wide rim mouthpieces reflect this. Today with the exception of some "brass band teachers" (especially in the UK) pressure is frowned on. Unfortunately, using pressure is quick and easy while developing lip muscles takes time - especially for older students.

Air pressure ("breath support") is probably less important on a french horn on Euphonium. The air stream has to push the lips apart against the lip tension. For higher notes a faster air flow or more tension is required.

I struggled with the Farkas method for three years. I faithfully did everything he recommends including his oval smiling pucker embouchure. I had no range & no endurance. In fact, I would feel faint after playing just a few notes above the staff. Nothing my my private instructors did helped me develop the range I needed to advance on the French horn. I decided to look to the high note specialists of the brass instrument world for help. I found a trumpet player in Garland, Texas with a unique & totally NON-FARKAS embouchure development system that changed my horn playing career. I now have chops to envy. I can play full 3 1/2 octave range with ease, good volume & SMOOTH CLEAR tone. Finally after so much useless effort on the Farkas system, I find help from a trumpet teacher! The system is called The Balanced Embouchure, developed by Jeff Smiley. His program is totally unique & can't be found anywhere else. I've shared it with three of my horn playing friends, including my private instructor. Everyone who has tried it is amazed at how quickly their range & endurance improves once they start it. The foundation of his program includes exercises in the extreme ends of the range -- roll-in exercises to develop upper range; roll-out exercises to develop the bottom. Then those exercises are followed with specific lip slurs to connect the top to the bottom in a continuous flex. The embouchure that finally emerges -- the BALANCED EMBOUCHURE -- can play the full range bottom to top to bottom in one continuous smooth motion. This system works. I'm living proof. For more information, search the web for The Balanced Embouchure. I have NO commercial interest in this program. I want to see other hoen players reach their full potential. Too many horn players have been hampered by the Farkas system. The Farkas system only works for a few, but not for all. The Balanced Embouchure works for every student who tries it.

For me, getting a clearer upper register came with lots and lots of practice. I had a big problem with the amount of pressure I was putting on the mouthpiece, which was making the higher notes sound pinched. After I got that fixed, I worked on pedal tones. If you work as achieving solid pedal tones, the higher notes get easier to reach.

Every time I hear someone quoting Farkas & his smiling pucker embouchure I just want to cry. This embouchure DOESN'T work for all horn players. The Farkas method is responsible for stagnating two generations of horn players. The other thing that makes me sad to hear is people talking about a "pressure problem" as if it were the cause of a poor upper register. Excessive pressure is the SYMPTOM not the CAUSE of a poor upper register. The real problem with a poor upper register is a brass player not knowing the "how to" lip mechanics of what makes a high note & what makes a low note. You (or your lips) must know the "how to's" to play in the upper register. A few players do it instinctively, often not even knowing how they are doing it. Farkas was one of those. But many horn players don't figure it out instinctively which often causes failure to achieve the upper register. And, of course, no upper register eventually leads to failure to progress. Farkas was a GREAT horn player and a great man, but he didn't really understand how he did what he did & he definitely didn't know how to teach others to do it. If you want to learn the "how to's" of the upper register, look to the high note specialists of the brass world: trumpet teachers. Trumpet pedagogy is decades ahead of horn pedagogy. Visit Jeff Smiley's website http://trumpetteacher.net/ . His Balanced Embouchure system is the ONLY thing that worked for me. I practiced my fanny off doing the Farkas method for years and all I got from it was frustration, failure and PRESSURE PROBLEMS!!! Only after doing Jeff Smiley's development system was I able to play clearly in the upper register without excessive pressure. (By the way, Farkas later admitted that pressure IS essential to playing in the upper register & that he regretted making such a big deal of the pressure issue.)
Valerie, happy come back horn player in Tacoma, WA

Just keep practicing your high range. Also, practice your low low range too. Pedal tones all the way! Practice the low notes will actually help your high range, and you'll also developed a greater range as a whole with better tone all around. Practice practice practice!

What they said. But a good idea is to practice often and not long, it seems to work for me. The last couple of days I've been trying that, and I've noticed that my lips don't get as tired by the end of the day, that way I can practice stuff a lot more than once a day before my lips die. To expand your range, go down and up as far as you can go and just practice it a lot and do tounguing exercises in each register and maybe some long tones.

You probably already know this, but I just found it out not too long ago, so I'm going to share it. With a double french horn (B flat and F, I don't know if there are any others, but I thought that it might be a good idea to specify), you can go a lot lower with the B flat side of your horn after you hit low low G (6 ledger lines below the staff on F horn) with the F side. I'm not too sure that this may be doing it correctly, but it sounds good and is still in tune so I don't worry about it.

Practice long tones everyday starting mid range and continue up by steps and every note will get a little easier everyday. Also, don't forget to use full amounts of air, higher notes require lots of air!!