Replacing an old thermostat with a digital one is a simple process that can be done in a few steps. First, turn off the power to your HVAC system. Then, remove the cover of the old thermostat and unscrew it from the wall. Take note of the wires and their corresponding terminals, and disconnect them from the old thermostat. Next, attach the wires to the corresponding terminals on the new digital thermostat and screw it onto the wall. Finally, turn the power back on and program your new thermostat according to the manufacturer's instructions. If you encounter any issues during the process, don't hesitate to contact the specialists at HVAC Alliance Expert for assistance with thermostat repair or replacement.