Wall heaters are typically gas- or electric-powered heaters that are designed to secure directly to a wall. Exactly how many clips and fasteners are used to secure a wall heater to a wall varies depending on the unit. To remove a wall heater, these clips must be removed, as well as their connection to the gas line that allows the heater to power your home. All of this must be done in a very specific way to avoid serious injury.
Shut down all electricity running to your wall heater (if you're using an electrical wall heater). If the unit has an "On/Off" switch, turn the unit off. For extra security, turn off the circuit breaker in your home's circuit box that is tied to the wall heater. Allow a few minutes for the heater to discharge any extra electricity it has built up once shut off.
Turn off the gas line that is connected to your wall heater (if using a gas unit). Somewhere on the wall heater (the exact location depends on the model) will be an "On/Off" valve for the gas line that allows your wall heater to operate. Turn this valve to the "Off" position. Also turn off whatever the source of that gas was (for example, use the shutoff valve on a nearby propane tank) and disconnect the gas line from the rear of the unit. Disconnecting the gas line may involve the use of a wrench, depending on the model.
Use either a screwdriver or a drill to remove the screws that are holding your wall heater onto the wall. Exactly how many screws depend on both the overall size and the model of the unit. Start on one side of the wall heater and examine the sides of the unit, removing any screws you find. Once removed, the wall heater will separate from the wall, and you can do with it what you want.