how to changew the thermo on a 94 cobra?

What do you consider hot? Putting in a 180* thermostat isn't going to make the car run any cooler. By the time the car is at 195*, the thermostat is going to be wide open, and flowing as much water as it can regardless of the thermo temp range. If you want to flow more water to the radiator, you have to get a Mr. Gasket high flow thermostat. Though I must warn you, once you switch to a high flow thermo, you're not going to have much for heat in the winter. The thermostat flows so much water to the radiator, hardly anything gets to the heater core.

Kurt