Where is the thermostat and how do you replace it on a 1991 FireFly?

Not familiar with FireFly, but most are 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 Clean both surfaces Replace thermostat and gasket Replace housing Re-fill coolant slowly to prevent an airlock Start engine and look for leaks Run engine to normal operating temperature with heater on Re-check coolant level