Can I remove specific incorrect Thunbnails?

I've looked through the forums for a few weeks trying to get tv series The Big Bang Theory to display correct metadata. I've been successful at renaming my media to retrieve the correct data with everything except this show.

At some point, the naming convention made it pull a XXX parody cover and title for every single episode, ha ha, except that my mom and son like to view that remotely.
I've cleaned up the naming convention to match thetvdb.com and attempted to re-scan metadata but the porn parody info still shows up when browsing that particular show.

I see many posts about removing thumbnails and such, but no direct info as to where they are stored. How can I safely delete a thumbnail and title and have it re-scan again?

Serviio V 1.4.1.2 Pro
Windows 8

[DenyAll]

Try pressing refresh metadata. If that doesn't work move the files to another folder (not in your shared folders), force refresh, and confirm that have been removed. Move the files back and force refresh again.

If the files reappear with the wrong covers, post the full path and file name for one of the files.