Hi,
Click on MY CONTROLS ...it should be up by where the messages, and new post links are. Go to MY CONTROLS. When you get there on the far left there will be a list of options. One says sometime like EDIT AVATAR ...click there. Then you can either link it to a picture or upload one from your computer.
If you upload it though, make sure its small. I've had trouble uploading most of the pics i like because there to big.
Good luck With it!
Leeana