Are you trying to change the avatar pic (the one that shows here beside your posts)? If so, make sure the size of that pic is no more that 53.7 kbs or 125x125 pixels.
Now, the picture on your profile page can be a bit bigger at 200x200 pixels or no bigger than 58.6 kbs.
You should be able to resize it in photobucket or in Paint on your computer.
