Warm the engine up to operating temperature before parking the Jeep on a flat, stable, level ground. Open the bonnet and loosen the oil filler cap, then position a drain pan under the sump. Remove the sump plug to drain the oil, being extremely careful not to get hot oil on you as it can cause serious burns. Once the oil has fully drained replace the sump plug with a new washer. Remove the oil filter, remembering to be careful of hot oil, and fit a new filter after smearing the rubber o-ring on the new filter with some fresh oil. Hand-tighten the filter a quarter-turn past snug, then fill the engine with fresh oil as per the manufacturer's handbook.