LRTimelapse 7.0 beta12
Win10

If I have an older Version of LRTimelapse installed e.g. in 'C:\Programm files\LRTimelapse 6'
then the installer removes this directory and replaces it with LRTimelapse 7' without any information.
All files or folders that I had added in the previous version is gone.
Only if the old folder name does not end with a single number (e.g. 'LRTimelapse 655'), then a new folder 'LRTimelapse7'
is created in parallel to the 'old' version.
I hope for me, that I had no important files stored in the 'LRTimelapse 6' folder.

That's a program folder, where usually no individual files are being stored. That folder is courtesy of LRTimelapse, not to put user files.
It's only possible to have one version of LRT installed at a time, not multiple versions in parallel. Just let the installer do its work. If you want to go back to LRT 6, just install LRT 6. If you want to try LRT 7, install LRT 7. Each installer will delete the other version. That's how it needs to be.