click on profile then on the top of panel it says information, preferences, signature, avatar. click on avatar.
You have options of uploading from your pc or from a URL
I've never uploaded one from my pc before so if your using say a pic of your boat, just browse for it by clicking browse I think.
or if it's a pic online. right click the pic then select properties, URL address should be there. highlight it then copy & paste to the URL bar for an avatar in your profile then save.
That should be you sorted