You can call up your picture gallery by going to "My Bildkontakte" and selecting the menu level "My pics". On top of the page next to each pic you will find a select field (except of the main profile pic). Select the option "As main pic" from the drop-down menu and then click on "change". This is only possible, if the picture was activated by our VIPs for the profile and therefore has a green marking (green bar at upper image border).
Please note as well that only visible pics can be set as main picture. Pictures that are hidden have to be activated first.
To delete the main picture you have to replace it by another one.