How do you change thermostat in a 2006 kia optima?

To change the thermostat in a 2006 Kia Optima, first ensure the engine is cool and disconnect the negative battery cable. Drain the coolant from the radiator, then remove the upper radiator hose connected to the thermostat housing. Unfasten the bolts holding the thermostat housing, take out the old thermostat, and replace it with the new one, ensuring the gasket is properly seated. Reassemble the housing, reconnect the hose, refill the coolant, and reconnect the battery.