How do you change thermostat in 06 Buick Lacrosse?

To change the thermostat in a 2006 Buick Lacrosse, first, ensure the engine is cool and then disconnect the negative battery terminal. Drain the coolant from the radiator, remove the upper radiator hose, and unbolt the thermostat housing to access the thermostat. Replace the old thermostat with a new one, making sure to align it correctly, then reassemble the housing, reconnect the hose, refill the coolant, and finally reconnect the battery terminal. Always check for leaks after replacing the thermostat.