How do you replace thermostat on 1998 Toyota 6 cylinder?

Should be located in a removable housing at the engine end of the upper radiator hose Drain about 1 gallon of coolant from the radiator Remove this housing Note how thermostat is installed in housing Clean both surfaces Replace thermostat and gasket Re-install housing Re-fill coolant slowly to prevent an air lock Start engine and look for leaks Run engine to normal operating temperature with heater on Re-check coolant level