If the footprint of the new thermostat is different from that of your old thermostat, there are a few options to consider. Your new thermostat may come with a wall plate that sits between the base of the product and the drywall. Wall plates will cover a wider surface, sometimes completely eliminating the need to do extra wall refinishing.
If you choose to avoid using the wall plate, there may be holes that need to be patched and sanded and paint that needs to be touched up. Use lightweight wall spackling compound and a putty knife to repair holes and sandpaper to create a smooth surface. Use a paintbrush to perform touch-ups. Allow the paint to dry completely before installing the new product.
Follow instructions to attach the base of your new thermostat to the wall. Using a level (it may be built in to the thermostat itself!) mark the holes for new screws and then pre-drill into the wall using the drill and a 1/8” bit (or recommended size). Use the screwdriver to attach the base of the thermostat to the wall.
Thermostat wires for a typical heating unit will be required to connect to the W and R spaces on your product. With the NEST product shown here, the straight copper wires are inserted into two plugs, rather than wrapping around screws.
Once again, follow directions provided with your product if your HVAC system is more complex.
The front of the new thermostat will simply plug into the base. If you’re using a smart home product, follow directions on the screen to set up the product, and then test it to be sure that it correctly activates your HVAC.