How do you change a thermostat?

I've got a 1990 Pontiac Sunbird. How do I change the thermostat? Do I need to flush the system?How do you change a thermostat?
First find out where the thermostat is located, usually it is where the radiator hose is on the top hose follow it to the end, and that will be where it is. Loosen the bolts and take it out and then flush out the system with water, put in the new one and tighten up bolts and let car idle and check for leaks.How do you change a thermostat?
Umm... There are a few things you need to know if try this yourself.



If you tighten the bolts back and the thermostat is not perfectly in place the casing can be forced and break.



Cleaning the contact surface perfectly is key.



Using a good gasket and seal is essential.



Do your homework on thermostats... Cheap is not good.



Good luck with the rest.