Simply log in to your Authory account, open the sidebar menu and then select "Settings". On the Settings page click the link "Edit my profile".
At the bottom of the "Edit my profile" page you can choose between a background color or a background picture. For the latter you can either use our extensive image library with thousands of high quality background pictures or you can upload your own. Please note that the ideal format is X pixels and the supported image types are JPEG, PNG and GIF.