Unplug the air conditioner from its power source. Carefully pull the plastic front cover of the unit on each side (let and right) one at a time to remove the cover. Remove any attached drain hose that is connected to the unit. Have an assistant hold the case, and slowly pull the unit forward until it is fully withdrawn from its case. Lay the unit on a lat surface.
View the inside of the unit's casing. Locate any screws used to fasten the casing to the studs or plates around the unit's casing, and remove such screws, using a screwdriver. Pry away any portion of the casing that has gotten stuck to studs or plates around the casing, using a wonder bar.
Pull the casing slowly out of the wall opening to remove it. Take extra care when handling the casing to avoid cuts that can be caused by sharp metal edges. Place the casing carefully on a flat surface.