How hard is it to do?

I watched my armorer's video and it seems easy enough.

Is it easy?

Remove handguards.
Remove gas tube.
Unscrew barrel from extension (torque wrench).
Screw new barrel into extension (torque wrench).
Etc.

Obviously you'll want to use an armorer's wrench, or whatever, but I believe a torque wrench would take care of the job just fine in case you didn't have one.  Just dont scratch that new barrel of yours.

Unscrew barrel from extension (torque wrench).

No, a torque wrench is only used for installing a barrel, not removing. Use a breaker bar or ratchet for that.

Huh?

I would get the good BARREL NUT WRENCH  and loosen the barrel nut.  then then barrel and barrel extension should come with out of the upper.  I would replace the barrel with the extension all ready installed.  This is the critical part and where the head spacing is set.  Put some lube an the threads and re-tighten the barrel nut.  35ft.lbs and then to the next hole that lines up with the gas tube hole.  A good idea is to torque to 35 ft.lbs., then loosen, repeat 2 more times, then do it the last time.

Armalite sells the good wrench.  You should have the receiver block set too.