In case you are still wondering; Top left of the main screen is your Identity bar (next to the big white Search box), with [ Friends ] [ Followoing ] [etc ]. Hover your mouse over your image, and on the Pop-up/Drop-down that appears, select Settings. That takes you to your account settings page, where you can change your image using [ Avatar and Theme -- Choose your identity ] Browse through the pictures for your avatar and profile banner and choose some you like.