Carefully separate the front half of the thermostat from the backplate by placing a small flat head terminal driver into the slots on the bottom face of the thermostat. Carefully unplug the cable connector which is plugged into the front half of the thermostat. Place the thermostat front half somewhere safe.
Follow the Wiring Diagram to do the wiring. Screw the thermostat backplate on to the flush box re-connect the thermostat cable and clip the two halves together.