I'm trying to remember what I did.
Maybe others can help me out.
What you will need is the thermostat and a new gasket for it.
You make sure the engine is cool, and then take off the cover where the hose connects to the engine. I think there are two bolts.
You remove the old thermostat and gasket, and then remove any excess crap that the old gasket left. Once that is all cleaned, you can put in the new one, along with sealing down the gasket, and then bolting everything back on.
Am I missing anything?