I couldn't work out how to do until I saw this from Monkeymax:Go to the top of this page, "Forum Actions" (Under the "What's new" tab), click "Edit Profile". In the new page look on the left for a box titled "My Settings". WIthin there is the option to "Edit Avatar". You can then upload it and save changes.
ahhhhhhhhhhhhhhhhhhhhhhhhhhhh thats been doing my head in for months !!