First off, is it automatic or manual trans?
1. Drain the gear oil (manual) or ATF (auto)
2. Remove both drive shafts (4x4 and rear wheel).
3. Disconnect the battery and then remove the starter.
4. Go under the truck and disconnect any wires, lines or plugs connected to the trans and transfer case. Be sure to remember where they go.
5. Disconnect the 4x4 and shift linkages.
6. Unbolt the cross member under the tranny and have a jack under the trans so it dosen't fall.
7. Unbolt the bolts connecting the bell housing of the trans to the engine. Pull back so that the trans input shaft has cleared and lower the trans.
8. Swap over the transfer case from the old trans to the new one and install oposite of removal.
If I've missed anything fill in the blanks. Also it couldn't hurt to go out and buy a repair manual for the truck. I use the Haynes 1980-1996 Ford Pickup and Bronco, I got it for 16 bucks at the local parts store.