ProjectMgr is accurate here. As long as you know that the thermostat is compatible with your heating and cooling system, then this will be a simple project. I can give you the basics, but, since each manufacturer has slightly different installation instructions, you need to read your manual. If you know how to turn off the power to the thermostat, then do that first. If not, then be very careful. It is probably low voltage, but you could ruin your new thermostat if you cross the wrong wires. Remove the screws holding the old thermostat to your wall so you can free up the thermostat. If the old thermostat has glass tubes containing mercury, make sure that you recycle it properly. There will be either 2 or 4 wires, depending on whether your heating and cooling systems are separate or one unit. Unscrew one wire at a time. Put a piece of masking tape over the exposed wire and label where it was attached on the old thermostat. Tie or tape the wires, so they don’t accidentally fall back into the wall. Once the old thermostat is totally disconnected, run the wires through the new wall plate and attach the wall plate to the wall. Screw it into the stud behind the drywall, or use drywall anchors. Connect the wires as directed by the instructions that came with the new thermostat, and then install any needed batteries. Attach the new thermostat to the wall plate. Turn the power back on to the thermostat and then program it according to the directions. That is generally the most challenging part. Follow the steps precisely, and you’ll do fine.