How do you replace the thermostat on an 03 highlander 2WD 4 cylinder?

To replace the thermostat on a 2003 Highlander 2WD with a 4-cylinder engine, first, ensure the engine is cool and disconnect the negative battery cable. Drain the coolant and remove the upper radiator hose connected to the thermostat housing. Unbolt the thermostat housing, take out the old thermostat, and replace it with a new one, ensuring the gasket is properly positioned. Reassemble everything, refill the coolant, and reconnect the battery.