See step 7 above in hang a mirror using hooks for information on how to install drywall anchors and how to remove unwanted drywall anchors.
How to hang up a wall mirror.
Lift the mirror into place and lock the two cleat hooks together.
Set the mirror down.
Hold the mirror against the wall at the desired position.
Finding a stud can be useful but not necessary if you have a strong enough hanger.
Use anchors if the bottom cleat isn t lined up over wall studs.
Mark the location of the top edge and the center of the frame.
Find a place to hang the mirror.
Gradually reduce your hold on the mirror until it is fully supported by the cleat.
They should fit together like jigsaw pieces.
Place a scrap piece of wood that is approximately half as long as the mirror is wide underneath the hanging wire on back of the frame.