Depending on the year and model of your Jeep vehicle, it may have separate or integrated high and low beam headlight bulbs. Generally if you can only see one bulb in the headlight housing, that means that your high and low beams are integrated into a single bulb that has a high and low output setting. Even if just one of the functions has stopped working, you'll have to replace the bulb to regain working high and low beams. If you're Jeep has separate bulbs for high and low beam functions, then you can replace only the defective bulb that has stopped working.
There are factory style replacements bulbs, and there are also off-road only high out bulbs that will project more light on to the trail in front of your Jeep. If you're vehicle is a trail only Jeep, these could be a good option for increased night time visibility.