I think you go to
Profile --> scroll down to the end of the page and you'll see
Quote:
Avatar Control Panel
Upload Avatar from your machine: "Upload Through Forum Profile"
Upload Avatar from a URL: "Upload Through Forum Profile"
Link to off-site Avatar: _________
Click "Upload Avatar from your machine," and then go down to the end of the page and click "Choose." The big thing is getting the file size right: right click on your file and click "Properties" and it'll tell you how big it is. It has to be less than 6kb and no more than 130 pixels wide by 130 pixels tall. Also, it won't tell you if your .jpg or .gif is too big.
I hope this helps you!
-Sam