On a 4 lamp system you have one high/low and one high on each side. The conversion installs headlights that accept a bulb rather than a sealed beam that is the bulb and glass housing in one package. You can get 55/60 halogen sealed beams for much less than the cost of a conversion kit.

Make sure you get a quality conversion kit if you plan to run higher than stock wattage or they may melt. Also, you should use a relay for higher than stock watts or you'll burn up the headlight switch.