On the Flex, the T-stat is located on drivers side end of engine up top. SO if your's is in the same place, all you have to do is slowly loosen housing bolts with a container below. Keep filling container (when close to full tighten bolts to stop flow) After flow starts to slow, open radiator cap to make sure all will drain out of T-stat housing. Then simply switch out T-stat and when tight, add fluid back in with vehicle running and heater on full blast to make sure heater core is full. If you lose any fluid add extra ( proper antifreeze required). If you're patient, you will lose little if any antifreeze, and find this is a very easy mod to do yourself.
Much harder on GM LS engines as T-stat housing is half way down block and requires about a gallon of fluid to be removed. EB guys are lucky!