New/Clean installation and import of old files and unser

Hello,

I got some problems with my nextcloud … collabora office doesn’t work, I can’t include dropbox folders, now I even can’t see the ‘external storage’ site (it’s just white), nextcloud talk doesn’t work properly, sometimes are some problems with letsencrypt certs and there are some more small bugs which isn’t worth the time …

And maybe it’s time for a restart … because my server is running since OwnCloud v7 (2015) and there a some ‘inherited waste’ which could cause this problems …

So, I want uninstall nextcloud complete (maybe apache2, too?) and install it new and clean. But then I wan’t to input all users with all of them files/contacts/calendars.
I don’t want to put the whole ‘data’ folder in the clean installation (if not necessary), but the cloud has 12 user and I also don’t want to copy all files/contacts/calendars manually. But in den data-folder is some waste (a lot of oc-files and folders), but I don’t know what I can delete.

Is there a manual to do this (with Ubuntu 16 and apache2)? I can’t find something like this …

No idea how to export all data to a new and clean cloud?