After you successfully logged yourself in, you find your surname in the main menu on the top right corner. Move the cursor to your surname and click on “My profile”.
Then you arrive at your profile and you can click on “Change photo” right below your current display picture.
In the dialog box that appears now, you find several pre-assembled display pictures you can choose from. You also have the possibility to upload a picture of your choice. Therefor click on “Browse” and select your picture. The picture should be quadratic, not larger than 1 MB and should be saved in one of the well-established image formats (jpg, png, or gif).
Click on “Update display picture”.