Open your hood and locate the upper radiator hose coming from the top of your radiator. this hose should go straight to the thermostat housing. You will need to drain the radiator and remove the hose. there should be three ten millimeter bolts hold it on remove the bolts and replace thermostat.
If you mean the engine coolant temp sensor it should be on the drivers side of the engine block. Follow your top radiator hose from the radiator to the engine block. near that you should see a sensor (it has a clip on it where the wires attach). I hope my description helps!
There is no cap for the radiator. To add anti-freeze to your radiator you have to fill it from the overflow. To find that trace a small rubber hose from the top of the radiator to what should be a plastic container