how to change rear shocks on 1999 Jeep Grand Cherokee

You must not have the new ones in hand or you'd see it's fairly straight-forward. Two nuts, two lock washers, and two stamped steel washers, then the shocks just slide off the bolts.

This isn't going to cause much trouble but it's good to be aware that when professionals replace parts with rubber bushings, they always set the vehicle down on the tires before tightening the nuts that hold those bushings. If front control arms are allowed to hang with the vehicle jacked up and the bushings are tightened that way, they will be in a permanent twist when it's set down on the ground. Bouncing up and down going down the road will twist those bushings beyond their design and cause early failure.