How do you replace Mazda 323 thermostat?

To replace the thermostat in a Mazda 323, first ensure the engine is cool, then drain the coolant from the radiator. Remove the thermostat housing by unscrewing the bolts and disconnecting the hose. Take out the old thermostat, clean the mating surfaces, and install the new thermostat with the correct orientation. Reassemble the housing, reconnect the hose, refill the coolant, and check for leaks.