How do you replace the thermostat located on a 1999 Toyota Corolla?

To replace the thermostat on a 1999 Toyota Corolla, 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 and take out the old thermostat, replacing it with a new one, ensuring the gasket is in place. Reassemble everything, refill the coolant, and check for leaks.