How do you change a thermostat on 4lt aerostar?

To change the thermostat on a 4LT Aerostar, begin by allowing the engine to cool and then disconnect the negative battery cable. Drain the coolant from the radiator and remove the hoses connected to the thermostat housing. Unscrew the thermostat housing and replace the old thermostat with a new one, ensuring the gasket is in place. Reassemble the housing, reconnect the hoses, refill the coolant, and reconnect the battery.