-undo bottom radiator hose off the thermostat housing, you'll only really need to undo the top clamp (thermostat housing is just behind where your water pump is)
-remove the 3 bolts off your thermostat housing
-remove the thermostat (it just pulls out)
-replace thermostat and make sure you get a new gasket for the housing, it costs around $2 for one.
NOTE: if the person who had it before you used gasket maker, make sure you clean it all off before putting the new gasket in. i used the new gasket plus a bit of gasket maker.. i dont see the harm.
-put it all back together in the reverse order... it shouldnt take more than 10 - 15mins, you'll lose a bit of coolant out of the head so have some ready to refill.
-top the water up, start the car, top up some more then bleed your system immediatley... then top up some more if needed.
dont forget to top it up some more.