Got to user CP at the top left.
Then at the left hand side under Settins and Options you should see Edit Avatar.
You can either enter a URL from a hosting site such as imageshack.us, or upload a file directly from you're computer. Hope this helps.
You have to get an avatar which is 100*100 pixels, or smaller, you need to upload it to a picture hosting site like this: http://imageshack.us/ http://photobucket.com/
and more.
Vox sucks
[10:14]<siku> magnificent sparkling vampire
[10:14]<siku> i love you edward