I was just wondering if anybody has any tips for relaxing your wrist and arms when playing, my wrist is always tensed up.

That happens to me, especially when playing really fast octaves and other things. If you know the peice well enough that it becomes reflex, dont conciously think about your fingers, let them do the work.

First sit down on a couch or something and just concentrate on relacing your arm/wrist for a few minutes. Then start playing something really simple - Hanon #1 for example - play slowly and lightly. Adjust everything about the music to the comfort of your relaxed wrist. This is something you`ll have to work at. Make sure you can `roll` your wrists and everything is limber. Then move up to a SLIGHTLY more difficult piece - you might want to even play one hand at a time at first, just to teach yourself to relax. Eventually your playing will be almost liquid. Remember, practice makes permanent. good luck!

Well when I play Harp study by Chopin my wrist are really tense

You definetely want to pratice one hand at a time, this way you can be very smooth with the selected piece. Usually, I find the tensing comes only when a piece isn`t familiar. Once the piece is memorized and extremely familiar to you, playing will come almost involuntary. Try it and let me know if that worked!! :-)