Here's where it keeps all that info, first you have to Show hidden files and folders, Hidden Files and Folders - Show or Hide
=File Folder Settings.
Then go to Computer, C (or what ever drive your OS is on),Users, Your Name, App Data, Roaming, Microsoft, eHome.
In the DVD cover cache folder you can delete the ones you want.
In the DVD info cache folder you can delete all of it and it will refresh itself the next time you open media center.
Then you can go back and deselect show hidden files and folders.