The thermostat is a temperature control device usually located in a housing attached to the upper radiator hose. hers how to replace it:
Open the hood and locate the vehicle's radiator.
Remove the vehicle's radiator cap and use a radiator pressure tester to check for leaks.
Drain out some of the engine coolant in the radiator so the coolant level is below the thermostat housing to prevent leaking when replacing the thermostat.
If necessary, remove the upper radiator hose.
Remove the thermostat housing bolts.
Remove the thermostat housing.