Napkin cabinet Advanced

Taking down mirrors off the wall? - how to win in mount and blade

If our house the previous owner had bought the mirror on the walls of the lounge (EWW, I know). We never take it off, but I finally had enough and are declining. How I can simply, without breaking them? Not that I am, I cut myself or make a big mess. Even after the establishment as getting the glue off to? I read using a razor blade, but not to the marks on the wall? Sand? Thank you.

We use our TV to the wall.