Shut off the power to the doorbell by flipping the appropriate breaker at the breaker box. Use a screwdriver to remove the plate that holds the NuTone doorbell in place.
Disconnect the wires from the back of the doorbell plate. Depending on the NuTone model, these wires could be connected by wire screws or a twisted connection. Remove the screws or untwist the wires as needed.
Remove the new button from its packaging, and attach the wires in the same manner they were attached to the old button. Place the button plate back where it was, and secure it with the screws.