Here's how I changed mine:
With a cool engine, place some newspaper below the car and a towel or two to cover the belts as much as possible.
I made certain the gasket was already on the new t-stat.
Loosen coolant overflow tank cap. Do not remove it. Loosen so your hear the pressure being released.
Squeeze top radiator hose with one hand as much as you can and while holding hose tight, tighten cap on tank. Let go of the hose. This gets most of the coolant away from the t-stat.
Remove three bolts. Pay particular attention to the thermostat and how it's positioned. Top and bottom. I read someplace that the the little hole (at least there was one on my replacement) on the middle rim should be facing the firewall.
Remove housing and quickly remove old t-stat noting the placement of the unit as it comes out. Up and down and position of little hole. Place new unit in and double check the position.
Carefully replace housing and press straight down to seal.
Put in the bolts and tighten them up by hand. I watched the housing seat while tighening the bolts. Hand tight but a torque wrench can be used.
Wipe up any fluid on the engine and fire it up. Look for leaks as it warms to operating temp. Be sure to run it to operating temp and let it idle for a few minutes. Turn on the AC too.
Took me about 15 minutes.
That should do it:-)