How do you replace the thermostat located on a 1992 Ford Ranger 2.9L V6?

Follow the upper radiator hose to the engine block where it is held by a clamp. This is the thermostat housing. The thermostat lies underneath. Other engine parts may have to be loosened or removed to have good access. Best bet is to get a chilton service manual (for step by step process) from your local auto parts store or visit your dealer. The dealer parts guys may be able to give you some information. Public libraries also have vehicle service manuals in the reference section. Check it out.