How do you correct a kiln that is firing around 50 degrees too hot?

Make sure the thermocouple extends into the firing chamber by the correct distance. A 1/8" wide thermocouple should extend at least 1/2" into the kiln; a 1/4" wide thermocouple should extend at least 1" into the kiln. If the kiln overfires by the same amount every time, lower the programmed temperature by 50 degrees or whatever temperature is necessary to compensate for the overfire. If the kiln is firing inconsistently, check the thermocouple wires. They should be securely connected to the controller and the thermocouple. Make sure the wires are connected to the correct color-coded terminals. If all of that checks out okay, then replace the thermocouple.