Have you got a Service Manual (SM)? There's some good stuff there on removing/replacing.
Look closely at the ones you have in the drive shafts now. Are the zerqs angled (forward/rearward)? Are your new ones angled? Make sure the zerq angles the same direction. I've learned it's possible to reverse that angle way too easily and then not get a grease gun on it - so you have to uninstall/flip/reinstall. The u-bolts (straps) will release the shafts from the jeep (except the rear of the transfer case; remove the companion yoke along with the drive shaft). You'll need to press the other side out following the SM. I put the transfer case in neutral so I can spin the axles - to get my wrench on the nuts. At least one wheel off the ground for the rear (and front if no locking hubs) again so you can spin the shaft to get a wrench on the nuts. The bolts holding the flange yoke to the companion flange (on the brake drum) can slide back into the brake cavity area. I stick my finger in one of the brake drum holes to put pressure on the bolt head to keep it from spinning (against the flange inside the brake drum). Image below from CJ2A thread on "Detailed Pic Of Inside Hand Brake Drum", pg 2:
https://www.thecj2apage.com/forums/detailed-pic-of-inside-hand-brake-drum_topic13605_page2.htmlYou may find that once the nuts are all loose, you might be able to spin them with your fingers. I put the nuts back on the u-bolts/brake drum bolts so they don't walk off never to be seen again.
Since two cups will now be loose (all except the companion yoke on back of the transfer case), they may fall off and the needle bearings may fall out too. Not much of a problem since your goal is to replace. However, a good practice is once the u-joint is free from the yolks, wrap tape around the u-joint so that those loose caps can't come off. Makes for a neater disassembly where you don't have to clean up all the tiny needle bearings. Doing this on the new u-joint will really be important as you don't want to lose those new bearings! Yes, it's possible to carefully hold it and rest it on the floor while getting into position, but the tape technique will help avoid additional work. I do it this way but have in the past had to pick up needle bearings, wash them off, insert them back in the cup and push the cup back onto the u-joint ( with a few choice words along the way).
Study how the caps are held on to the shaft ends. Most likely it's a snap ring. Be careful removing. There's a plier made for this but you can also use a screw driver or needle nose pliers - carefully. They can easily go flying.
Run some sandpaper inside the rings that hold the cups - concentrate on the outer part above the snap ring as the most buildup will be there. There could be rust and crud that will make inserting the new cups difficult. Nothing wrong with a squirt of WD-40 or other penetrant during this cleanup, just wipe off the excess so you don't have contaminate trying to drip its way into your new u-joint. There should be no paint or crud where the caps will go - they're snug and anything on those surfaces could cause binding.
I'm sure there's more than one way to install a u-joint but now the easiest way to explain it, other than the SM, may be to google and watch a couple of videos. I DO wrap tape around the opposing cups while I'm pressing the other two into place.
Torque values are in section L, 15-18 lb.-ft. In the back, section U-55, TORQUE SPECIFICATIONS, the u-bolts are 15-20 lb-ft and the flange bolts are 20-30 lb-ft.
