Should probably try doing a search for "thermostat."

Pretty simple job, it's the small bell housing attached to the upper radiator hose at the front of the engine. You'll want to remove the coolant expansion tank cap, drain the radiator (at least partially), and unbolt the three bolts securing the housing. Dig out the o-ring with a small pick, remove the thermostat, and install the new one+new o-ring. The small ball valve on the thermostat goes at the highest point (usually on the block side of the housing).

The real question is - why do think you need to replace the thermostat?