Answers

They are tough to take off. If it's glued to drywall, you can use a prybar to rip it off from the drywall. Note: You will more than likely need to repair the drywall when you're finished, if you are going to have a finished wall. Go slow or you'll break the mirror. Also, wear safety glasses and gloves - a must.

Here are some helpful steps to make the process safe:

http://www.lowes.com/creative-ideas/bed-and-bath/remove-a-bathroom-mirror/project