This article was blatantly stolen from the SCORRS site, hope they don't mind. I did edit it a bit.
New Model Army Disassembly Instructions
by Craigius
Here is how I disassemble my 58's and so far I've done it about 38 times in the last 4 months. Been cutting down the barrel, polishing and the like. Just have to put everything back together before I go to bed at night. Anyway I've included a diagram for you.
Remove the Cylinder (part 5)
Take the grip panels off. (parts 44 and 45)
Take out or back off the mainspring tension screw. (part 53)
With the revolver laying on a bench, take the mainspring (part 20) out by drifting the base to one side out of its slot (with a brass tool).
It will pop out, don't have your hand or fingers under it. Remove from under the hammer if it didn't come completely out.
Remove the trigger guard (part 26 and 31)
Remove the trigger/bolt spring (screw 35, spring 19)
Remove Screws 37 and 38
Remove the trigger and the bolt. (parts 10, 12)
Turn the revolver over onto its right side. Push the hammer down until you see the handspring screw (part 52). Unscrew it and slide the hand and spring out.
The Hammer can now be removed, upward.
Double click the diagram to enlarge it.