Under the banner picture of the "Rig of the Month" there is a row of selections,
select the "User Control Panel"
Once in that area, on the left hand side you will see a list of "Options"
Then again under the "Options select "Edit Avatar"
At this point you will need to have a suitable picture that is the correct size and then select the browse button and locate the picture on your computer.
Also while in your profile there is a selection for signatures and profile updates to put in your location and other information you would like to tell the group
Hope I helped