How do you replace a thermostat in a 1995 Subaru legacy?

To replace the thermostat in a 1995 Subaru Legacy, first ensure the engine is cool and then drain the coolant from the radiator. Remove the upper radiator hose from the thermostat housing, unbolt the housing, and take out the old thermostat. Clean the housing surface, install the new thermostat (making sure the jiggle valve is positioned upward), reattach the housing, and reconnect the radiator hose. Finally, refill the cooling system with coolant and check for leaks.