what is the easy was to replace a thermostat on my car 96 ford probe gt

There's only one way: Drain the coolant, remove the bolt securing the coolant pipe into the thermostat cover, remove the cover taking care not to jam and break it, remove the thermostat, taking care to remember the orientation (which way it went in), install the new 'stat taking care to have the 'jiggle-pin' on top, reassemble everything using new O-rings (a little oil or grease on the O-rings aids in assembly). Use the correct heat 'stat, don't be thinking that cooler is better - it's not. If your engine gets hot idling, first thing I think of is that the cooling fans aren't working, not that the thermostat's bad, but it's a possibility. The cooling fans should cycle on and off automatically, but if the engine's getting hot, they should stay on until the temp goes down. In your model car, it's not unusual fro the lower part of the radiator to clog up, FYI..