KitchenAid Electric Cooktop; burner always on "High"

The triple burner, once is on, always heats on "high"; there is no way to have it at "low", or "medium", so it’s not usable. It seems that the device under the know that controls the burn is broken. On the KitchenAid website (not user friendly…) there are a few kinds and part numbers of the switches. Which one will work? Is it difficult to replace the part myself? How do you remove the top? I will greatly appreciate any help I can get from the forum members. Thank you!