I still have the very old version of Hoster

[Roy Dennis]

Don't just delete them. Uninstall while connected to the internet and follow the procedure, when you see the upgrade or remove option, select remove and that should automatically free up your registration.
According to the info on this page: http://www.mtu.com/support/hoster-versions-5.htm
If you scroll to the bottom it shows a list of all the version that are user move.
more or less all versions down to 3321a.
For the latest version see: http://www.mtu.com/upgrades/hoster.htm
If you do experience any problems then you would have to enter a support ticket for a re registering.

The list will also tell you which versions will run on which windows versions.