How do you change the thermostat on a 1997 4Runner?

To change the thermostat on a 1997 Toyota 4Runner, first, ensure the engine is cool and disconnect the negative battery terminal. Drain the coolant by removing the radiator drain plug, then remove the upper radiator hose connected to the thermostat housing. Unbolt the thermostat housing, replace the old thermostat with a new one (ensuring the spring side faces down), reassemble the housing, and reconnect the hose. Finally, refill the coolant, reconnect the battery, and check for leaks.