My server does not update added files anymore and more

Unfortunately, it won’t. Because the old Plex server version that you are using won’t get patched in any way, except by way of releasing of a new Plex server version – which won’t run on your old Windows version.

With proper preparation and calm step-by-step action, you can do it too.
See for example Attempting to move Plex Media Server settings and database to new windows server - database error - #3 by OttoKerner

Don’t forget to export your Registry data, for a truly seamless migration. https://support.plex.tv/articles/201539237-backing-up-plex-media-server-data/