Probably you "tablet" has a folder to cache album art.
For WMP it is
%localappdata%\Microsoft\Media Player\Grafikcache\LocalMLS
Delete the whole folder LocalMLS - WMP will recreate it.
If your tablet has a different player, you would have to look for that player's database/cover cache ...
In WMP it is easiest to update files like this:
Delete the files from the database only
Use Extras>Restore deleted elements.
Or with any other player: delete the files from the player and then invoke an update of the database.