thanks.
I mean CONTACT RELATED setttings.
Reason is: after several tries to set up “groups” etc in contacts back some months ago, there seem to be those groups still existing somewhere, even if I deleted them in the webinterface or on the clients. So I am trying to find a fresh start for contacts, also to be able to exactly determing in case i have to troubleshoot with community.
The contacts app only supports the categories field in the vcard rcf, which means the groups are only stored IN the contacts. So if you export and reimport again, you will absolutely get the same data 
Otherwise, truncating the oc_cards and oc_addressbooks table in the database is enough
So that means I would have to work within the database (mysql database) which is stored on my hosted enviroment, its not just some files which i can delete or edit via ftp, right?
No, you were asking for an easy way to reset your entire installation. The database is the quickest
Otherwise deleting the addressbook in every user you have will have the same behavior 
Getting back to deleting al data for adress books (including all groups within contacts etc):
i found out its quite easy to access the database on my hosted enviroment. So I will just delete the mentioned files oc_cards and oc_adressbooks – and probably oc_adressbookchanges as well, right?
thanks!
oc_cards and oc_addressbooks should be enough, I don’t have/know the others 
Remember to make a full backup before!
