Just to add to what the others have said:
- you will want to remove the fan and fan shroud in order to have better access to the thermostat housing
- if the housing is plastic buy a new one
- buy a new water pump unless you have a record of it being replaced in the last 60K, it's directly below the thermostat so you can save time and future trouble by doing it now.
- check your tension and idler pulleys for bearing noise and play, probably a good time to do them also
- check the serpentine belt for cracks
- if you have no record of the radiator being replaced this is a good time to do that, pulling the radiator also makes the whole job a breeze because of the extra room afforded.
Fan - 32mm reverse threads, you will probably need to make, borrow or purchase a tool to hold the water pump pulley still while breaking loose the fan clutch threads. Occasionally a healthy dead blow hammer tap on the 32mm wrench will get the job done.
It's not a difficult job as long as you go about it the right way, have the correct tools and remove the fan and shroud. Trying to shortcut it will result in frustration and sore hands.
Understeer.com is a local guy who sells all of the parts mentioned, he stocks decent quality stuff (much better than the fail-prone-poo of the chain stores)