A partial re-post from another thread...
Look where the radiator hose goes into the block. Not sure if it is the upper or lower radiator hose. Just went out and looked at mine. I assume it is lower one. There is a flange bolted to the block that the hose connects to. Just remove the flange and the thermostat will come right out. You don't need to remove the hose from the flange. Go to the local ports store and pick up a new thermostat and flange gasket. Be sure to catch the anti-freeze to re-use, or buy new anti-freeze while you are at the parts store, because you will drain all of the coolant when you remove the flange.
Can someone that has replaced a thermostat on their KJ verify if it is the upper or lower hose? I haven't had to replace one yet on mine.
Here is the lower hose with the flange looking up from beneath the car...
