It may or may not be too big, I'm not sure. But your a smart kid, I think you would be able to shrink it.
Go to User CP
Edit Options
Go to the bottom, click 'Change Avatar'
Go to the bottom of that, find the browse button, and then find the pic on your HDD. Then go to where there is a button above that that says 'Use Custom Avatar'. click that, then click changes. And then you are all set. It will tell you if it is too big.