How do you replace a thermostat on a 2002 dodge ram 1500?

Should be located in a removable housing at the engine end of the upper radiator hose (on a 4.7 L engine, it's at the engine end of the lower radiator hose in removable housing)

Drain about 1 gallon of coolant from the radiator

Remove this housing

Note how thermostat is installed

Clean both surfaces

Replace thermostat and gasket

Re-fill coolant slowly to prevent an air lock

Start engine and look for leaks

Run engine to normal operating temperature with heater on

Re-check coolant level