It's easier to do this from your PC or Mac. Go to 'ipadforums.net' and then click on 'User CP' (User Control Panel). There you'll find a whole load of options - include 'Edit Avatar'. Click on that and you can choose from a whole range of preset avatars or upload one of your own.
It can - just about - be done from the iPad if you don't have easy access to a PC, but it's more complex and so that's why we recommend using a PC or Mac if there's one available.
Let us know if you have any problems...
Tim