How do you change the thermostat on a 2001 Pontiac Aztek?

To change the thermostat on a 2001 Pontiac Aztek, first, ensure the engine is cool and disconnect the battery. Drain the coolant from the radiator, then remove the upper radiator hose from the thermostat housing. Unbolt the thermostat housing, take out the old thermostat, and replace it with the new one, ensuring the gasket is properly aligned. Reassemble everything, refill the coolant, and reconnect the battery.