How do you replace a thermostat on a 2001 Pontiac aztek?

To replace the thermostat on a 2001 Pontiac Aztek, first, ensure the engine is cool and disconnect the negative battery terminal. Then, drain the coolant from the radiator and remove the upper radiator hose connected to the thermostat housing. Unbolt the thermostat housing to access the thermostat, replace it with a new one, and reassemble everything by reversing the disassembly steps, ensuring to refill the coolant and check for leaks afterward.