Hi summerflower,

Once you've chosen your picture (has to be between 65 and 80 pixels - or smaller)

1/ click on "My Profile"
2/ click on "Edit Personal"
3/ scroll at the bottom of the page (it's the avatar section)
4/ click on "upload your avatar"
5/ click on "browse" (then select the picture)
6/ click on submit

You might need to refresh your browser afterwards, as the avatar might not show immediately.

Hope that helps.