No it isn't necessary. Sometimes the old micros seem hard to get out from either not finding the couple of screws that hold them in, or even with the screws out they sometimes will be held up with the accumulated grease.
Usually there are two screw in the top going through the bottom of the cabinet. Some units will have two long screws hidden under the front grill work. The screws run horizontally back to the metal bracket that is mounted to the wall. Let us know what you have or what you find.