Use my advice at your own risk. I will not be held responsible for what you do to your vehicle.
For Jeep Cherokees with a 4.0 engine; (if you are standing in front of the vehicle looking back at the engine compartment) the spark plugs are on the left side / the same side as your battery. What look like spark plugs on the right side of the engine are actually your fuel injectors. On the exact opposite side of the engine block, all 6 spark plugs are held in place with a long rectangular box (called a coil pack) that has 3 small raised boxes on it. The coil pack is the length of the engine block and about 1 1/2 wide. There are 4 large approx 1/2 bolts that hold this coil pack in place. There is a plug on the back end / closest to the fire wall where you can upplug this coil pack but I couldn't unplug it.
Simply, remove the 4 bolts holding the coil pack in place, lift the coil pack away from the engine block and the spark plugs are exposed. The boots that attach to the spark plugs are "fixed" in to the coil pack. Replace your spark plugs some type of using anti-sieze compound, adjust your gap, and torque to 19 lbs. NOTE: use dielectric grease on plug boots and coil pack ends of wires. can also be used on plug in bulbs.
The above answer is great but if they are platinum plugs don't bother setting gap because you usually don't get a spec anyways and you do more harm than good. The gap is preset.
Depending on your year of Cherokee, I know the 1991 and newer Cherokees use Champion RC12LYC, Autolite 985, and Denso QJ16HR-U with the 4.0L 6 cylinder engine. On my 2000 Jeep Grand Cherokee Limited with a 4.7L V8, I used Champion Copper Plus RC12MCC4. These are the plugs that the manufacturer calls for. No other plugs should be used. (If you don't believe me, search the internet) Learn how to change the spark plugs on a 4.7L V8 (SEE LINK BELOW).
Changing the spark plugs is a relatively easy job which can be done by anybody with slight mechanical knowledge. On a Jeep with the 4.7L engine, the intake needs to be removed. The coilpacks can then be removed, and then the spark plugs can be removed and replaced with new ones. The job should take about 1-2 hours. See the related link below for detailed instructions.
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