Welcome Abdelilah, a very easy solution and welcome to Fine Art America. Look in the upper right your name appears on the header bar. Hover over that and it will take you behind the scenes if you scroll down behind the scenes you will see an icon profile photo. Or you can access from Profile Page or and Behind the Scenes. Easy as that, upload a photo for your avatar or design. And you also can update your bio as well. It does not matter which you use they all work and easy access to make update and changes.
Most members work directly from artistwebsites and others do everything from the actually Fine Art America and the Pixels page accounts, they are all user friendly. Once you set everything up you will see how easy getting around is.
Always make sure you are signed into your account to make changes or upload. Also, behind the scenes is the actual default page settings you can have viewer see your opening page as your gallery page set up or they can view the opening page as images. There are many features behind the scenes which will help you be successful with your galleries.
Cheers, Michael Hoard Principal Actor, Artist and Photographer