How do you change a thermostat in a rover 400 diesel 2ltr?

To change the thermostat in a Rover 400 diesel 2.0L, first ensure the engine is cool and disconnect the battery. Drain the coolant from the radiator and remove the upper radiator hose connected to the thermostat housing. Unbolt the thermostat housing, take out the old thermostat, and clean the mating surfaces. Install the new thermostat, reassemble the housing, reconnect the hose, refill the coolant, and reconnect the battery.