how do I change the thermostat on my 01 F150 4.2L?

Follow upper radiator hose, goes right to it. Let the engine cool off, then drain it down about a gallon, there is a draicok on the bottom of the radiator, then follow the upper radiator hose to the engine, there you will find the thermostat at the end of the hose, unbolt the two bolts. leave the hose attached to the housing. Scrape old gasket from both mating surfaces, install new thermostat, spring towards the engine. install the gasket, snug the housing bolts! Not to tight and bring the housing down evenly. refill the coolant and that's it!