How do you change out a thermostat on a 2004 GMC savanna van?

To change the thermostat on a 2004 GMC Savanna van, first ensure the engine is cool and disconnect the negative battery cable. Drain the coolant from the radiator, then remove the hoses connected to the thermostat housing. Unbolt the housing to access the thermostat, replace it with a new one, and reassemble by reversing the steps. Finally, refill the cooling system with coolant and check for leaks.