A hoist makes the task very easy..
No trolley jack or bottle jack spices things up a bit.
The object is to lift the chassis away from the front axle, as PUK suggested the project-jk write up is very good and has all the instructions.
a trolley jack will make life very easy, just supercheap special will do just fine.
2 ppl make for easy work also, just remember a compressed spring is nasty, but you should be able to lift the tub, and lower the axle in such a way the spring comes free, putting the longer one in if you dont have the tub lifted high enough will be a problem.
I did mine on a hoist so i can not speak from experience on the ground. But with the front and rear axle you will find when it is at it's lowest point with the shocks disconnected you might need to push down on the side your doing to slip the spring in.
Not a difficult job really, just need to be mindful of handbrake cables, brakelines and the diff breathers etc.
it's all in the project-jk write up.