1988 Jeep Cherokee Ignition switch

Electrical problem
1988 Jeep Cherokee V6 Four Wheel Drive Automatic 160, 00 miles

How do you go about changing out the ignition switch in the steering column? The gas guage does'nt work right anymore. We have changed out the whole pump and sending unit in the tank, chased down all wires to check for a break somewhere, and even changed out the instrument panel, and still the level shown is about the same as when we started. It never goes to full when you fill it up. It stays around half a tank. So we decided that we need to change the ignition switch. It is sticking anyway. Have you any suggestions? Thank you. Mike.