Migration/import/maintenance on shared host _W/O_ occ

tl;dr: how to do anything when you can’t use occ command?

I intend to migrate my current OC installation to NC, but so far all research turns out to require occ at some point (except https://help.nextcloud.com/t/migrating-from-owncloud-to-nextcloud/551/8, but on that one later)

I hava a shared hosting environment without shell access!
the closest to that is using ftp and curlftpfs to mount it locally, but that still doesn’t help with occ (at least it doesn’t with my current OC installation).

the help topic linked to above just says

Trigger the update either via OCC or via web.

well … how to do this “via web” is nowhere explained – the “Admin Docs” section on the mainpage just links to blogs and videos (what is it with videos which take hours to explain how to cook an egg???).
and there’s a 250 pages PDF – which still only refers to occ, at least I find no hint on how to do anything “via web”.

so, to make it short: how do I import data from an existing OC installation to a new NC installation WITHOUT using occ?