I'll be doing the same thing in the next couple of months. The link below has several tips and I think I'll try the suction cups first before giving in to tape and prying it off.

The amount of damage you'll have on the wall will depend on how much, and what type, adhesive the installer used. Most damage is usually hidden by the new mirror.

Here is a link that might be useful: Removing mirrors

Does it have any mechanical fasteners or does it appear to be held up only by adhesive?

On DIY shows when they remove mirrors they cover the entire mirror with tape or heavy contact paper so that if the mirror breaks it doesnt go everywhere. Also heavy gloves, safety glasses and long sleeves and pants for protection.

Do you know how it's attached, and do you care what condition it's in when you're done?

Some mirrors are attached only with screwed-in clips, and with those you just unscrew the clips starting at the top and lift the mirror out of the clips at the bottom. That's the ideal.

More likely it's glued to the drywall and it can be easy or nightmarish to remove depending on how liberal the installers were with the glue. Two or even three people are needed for this operation. If you don't care if it breaks, cover the entire surface of the mirror with at least one layer of clear contact paper or duct tape; if you're hoping to save it, use 3" wide masking tape as it's somewhat easier to remove than contact paper or duct tape. Then pick up a roll of braided, uncoated wire at the hardware store and cut a length twice the width of the mirror. Piano wire also works if you can get it. Put down a heavy dropcloth, wear gloves, long pants, long-sleeved shirts, sturdy shoes, and safety glasses (no, regular eyeglasses do not count). Two people stretch the wire between them and slip it down behind the mirror, then start pulling it back and forth in a sawing motion, pulling downward at the same time. The third person should stand ready to catch the mirror as it begins to move away from the wall. If there's a lot of glue this is a slow process, if there isn't much this can go very quickly.

If the mirror butts against walls on both sides (is in a niche) and you can't get a wire down behind it, you'll probably have to break the mirror. After taping, use a rubber mallet to gently break the mirror into pieces beginning at the top corners. As you break up enough glass that it starts pulling away from the wall, use a utility knife to cut the tape so you can remove that section and drop it into a cardboard box inside a trash bag. Some sections won't want to pull off the wall and a wide-bladed, rigid taping knife is useful for wiggling down behind that section to pry it off.

The condition of the wall afterwards can vary from patches of glue on the surface of the drywall (cut/scrape away the paper with the goo on it and skimcoat with joint compound) to big holes where the mirror pulled the drywall right apart (happens more often at the bottom as the weight of the mirror falls forward)! For the latter, if they're bigger than about fist-size, even up the holes by cutting them back to the closest studs with a drywall saw and patching in new drywall. Smaller holes can be patched with rigid metal-mesh drywall patch kits from the hardware store or home improvement center (IMO they work better than the flexible fiberglass ones).

You might be able to rent those suction cups at a tool rental place to give you handles to help with moving it off the wall.I have seen them tape up the mirror in case it breaks in the process. There could be mirror adhesive behind the mirror in strips on the wall. Think zig zag pattern and that could have damaged the wall enough to need some touch up. Then again the glass might only be mounted to the wall with those mirror clips or a long track on the bottom.

You could take a glass cutter and score it down the center and across,AFTER taping the area where you do not score.Think of it as a package and your score lines the ribbon in side to side top to bottom. Tape the four squares off leave ribbon area clear to score on. But if you are not comfortable with glass cutter it might just make it harder for you.

Have more then just one person to do this as you will run out of hands needed on board. Wear eye protection just in case. Cover your counter with throw rug. Being prepared for the worst will make it NOT happen and all will go well for you.

Chris

Hehehe I type too slow. Sorry for the repeat.

Boysrus2, thanks for the mention of where to buy the suction cups!

Here is a link that might be useful: suction cups

Thanks for all the replies. Our mirror is boxed in on 3 sides, only the bottom will be accessible. We're taking the counter and cabinet out first. No screws or clips so just glue on the back holding it up.

I was also busy googling so sounds like taping it all up and then giving it a whack (rubber mallet!!) should do the trick. Those suction cups sound good like a good option too. I'll let DH decide.