Then down at the bottom it will say CHANGE AVATAR - click that
You will be shown a page of the avatars, or little pics. If you don't like the ones on the first page keep going, there are 9 pages of them. Click the little box by the pic you want, then click SUBMIT CHANGES and it will say THANK YOU FOR UPDATING YOUR PROFILE! and the pic should be showing up in your posts.Also if there is particular pic you like that is not in that list offered by the site, one of us can make one for you