So far we had a SQL Lite database. With many users. Now we have switched to a large database. Is there a possibility that I export the users (more than 70) from the old database (owncloud 9) and import them into the new database (owncloud 10)? or do I have to create the new users manually?
you can try to use the data_exporter https://github.com/owncloud/data_exporter (requires an upgrade to 10 first)
or try https://doc.owncloud.org/server/10.0/admin_manual/configuration/database/db_conversion.html