Hello,
I'm sorry not to speak German...
If you mean to upgrade from an older version (free 3.5.9) to the pro version 3.6.6, don't worry for all your datas.
Just install the pro version (and NEVER uninstall iCagenda free); The script install will automatically upgrade your version to Pro, and nothing change for your data
In all cases, after purchase of Pro version (if you don't have yet) never hesitate to use the Pro ticket support for any question or help request
Best regards,
Cyril