Should be in a housing just at the motor end of the upper radiator hose. Trace the upper hose down under the alternator.
Pull the hose off (be sure you have a way to catch the coolant first!) Then you unbolt the thermostat bolts and pull out the thermostat. REMEMBER which way it goes---the part with the "nose" points toward the radiator. Then clean both surfaces of the housing really good, and put on a new thermostat gasket. You can seal it with some light white grease, but just enough to make the gasket stick. Don't use goopy silicone sealant! Tighten the bolts but don't go crazy. Just enough to strain the muscles in your arm using a 3/8 drive wrench. Do NOT put your back into it. NICE and SNUG. Now you have to fill up the plastic reservoir tank. Then you run the engine for for just 30 seconds or so, then shut it off. Now you have to find the BLEED SCREWS and open them up so as to let air out of the cooling system. Then close the air bleeds. Repeat this filling up and running the engine briefly until coolant comes out of the air bleeds. Then top off the reservoir tank.
I think one air bleed is by the pipe where you put in the oil. Once you find it, look for another one like it. Sorry I don't have a manual for your car.