how do I locate and change my thermostat

Is the cooling fan running?

The problem probably isn't the thermostat, but sounds like your cooling fan isn't working. Especially, as you say, it cools down once air starts moving thru the radiator again at speed. But if you do wind up changing the thermostat, be mindful of the "clocking" marks on the gasket to match up with housing. Otherwise, it will leak for sure.