Option 1: if you want to delete all your personal data (owned, rated, wished, tagged, etc...), you just have to delete your coollection file.
Option 2: if you want to delete some scanned files, use the menu "Tools->Manage your video files->Batch delete several file associations".
Option 3: if the location of some files has changed, use the menu "Tools->Manage your video files->Batch edit several file associations".
rudi47 wrote:How do I remove my owned movies, so that I scan my files again, as they have moved to another folder?
The third option (edit) seems to be the best in your case, you won't even have to scan again. For example if your files were inside "C:\Movies" and they're now inside "D:\Videos", you'll simply ask the app to replace "C:\Movies" with "D:\Videos".