To safely remove a mirror, cover the front of the mirror with packing tape, and wear safety goggles, long-sleeved clothing and gloves. Soften the glue along the edges of the mirror with a hair dryer set to the lowest setting. Cut piano wire so it is 1 foot longer than the mirror. With an assistant, place the piano wire behind the top edge of the mirror. Use a sawing motion to cut through the glue.
At the bottom of the mirror, work carefully to support the mirror to prevent breaking it. Repeat the sawing process from the opposite side of the mirror if it doesn't easily lift off the wall. If clips are present, leave two clips on the bottom edge of the mirror while sawing through the glue.
After the mirror is loose, remove the clips to release the mirror. Alternately, insert shims along the edges of the mirror, and use a pry bar to gently loosen the edges of the mirror.
Place a shim behind the pry bar to prevent damaging the wall. If the mirror is very large, heavy or difficult to remove, consult a professional glass company to assist with the removal, or use suction cups designed to remove mirrors. After removing the mirror, wrap it in a soft cloth to prevent breakage.