all depends on how savy you are and the tools you possess.
if you installing a lunch box locker, it is as simple as pulling the shafts out, removing the center pin, and spyder gears and then sticking the locker inside the carrier and done. (this is abbreviated install instructions)
a full carrier locker, which the true trac is, (tech the true trac is not a locker, it is a Limited Slip Differential, it will never lock up 100%) you will need to strip the diff of all components and then reinstall the gear set as if it were new. some people simply swap the gears to the new carrier and re-use all the shim packs, I am guilty of doing this in a pinch, but I've also chewed up gears doing this. At a minimum, you need to check your gear pattern after the swap and then adjust the carrier and or pinion to get proper pattern and backlash.
99% of the time, I am able to reuse is the pinion shims with out changing them.