Almost all AKs made since the early 1960s have pressed and pinned barrels. To change one of these barrels you would need a 20T hydraulic press, a fixture that can hold the rifle for pressing, a drill press and headspace gauges. First the old barrel must be pressed out of the barrel trunnion. Then the new barrel pressed in to the point where the headspace is correct. Finally a hole has to be drilled through the hole in the trunnion, across the top of the chamber portion of the barrrel inside the trunnion and the barrel pin would then be driven in. During the pressing in of the new barrel, it has to be held in the proper position so that the front sight and gas block which are mounted on the barrel align with their counterparts on the receiver/trunnion.
The earlier, "classic" AK, the Type 3, has a threaded barrel screwed into the milled receiver and to change one of them would need a lathe and or shims to adjust the timing.
Drue