@tuxxus You can either export and import them via the web interface. That's how I did it, because I used the opportunity to start with a fresh installation of both the operating system and Nextcloud, or you can migrate your !ownCloud directly to !Nextcloud and keep all the data, users, shares, etc. It works the same as a update to a new ownCloud version. Here you can find a detailed description how to migrate an existing ownCloud to Nextcloud: https://nextcloud.com/blog/3-reasons-to-upgrade-your-owncloud-instance-to-nextcloud-and-how-easy-it-is/
3 reasons to upgrade your ownCloud instance to Nextcloud and how easy it is - https://gnusocial.de/url/3950167