How do you replace a thermostat on a 2004 Chevrolet Classic 2.2 ecotec?

To replace the thermostat on a 2004 Chevrolet Classic with a 2.2 Ecotec engine, first ensure the engine is cool and disconnect the negative battery cable. Drain the coolant and remove the upper radiator hose from the thermostat housing. Unbolt the thermostat housing to access the thermostat, replace the old thermostat with a new one, ensuring the gasket is in place, and reassemble the housing and hoses. Finally, refill the coolant, reconnect the battery, and check for leaks.