Replacing a hose-
If your using pipe thread, its probobly time to upgrade to a newer model!
That being said it is a very easy proccess and besides the previous post here is a couple more tidbits.
Some 2nd stages have unique fittings, ie Scuba Pro, most of there newer 2nd stages have spindle type fitting and you are suposed to use a special SP tool, but you can get by with a channel lock plyer, but be gental its plastic.
For the male fittings that go into the first stage use just a touch of lube, I reccomend cristo lube, make sure there is no dirt or hair on the oring and it is in good condition, tighten just a touch beyond finger tight. For replacing the hose that goes to the second stage check the female fitting, there is a oring there that can be cut by the second stage if not done gently.
Good luck and I think that all divers should be capable of changing hoses on the spot if need be.
JUMBO