Hi Hardworms,
If you click on 'User CP' then click 'Edit Avatar' you get the option to choose a 'Pre-defined Generic Avatar' or a 'Custom Avatar'.
The pre defined is simple enough. If you have your own custom avatar simply browse to where it is stored on your computer then click on upload.
Hope that helps.
Edit - Please be aware of the maximum size of picture you select for an avatar. On BCUK the rules state 'The maximum size of your custom image is 100 by 100 pixels or 58.6 KB (whichever is smaller).'