You asked "how hard is it to change a barrel?".
Here is the short answer: IF you have the proper tools (frame blocks and wrench, the proper barrel vise blocks, the forcing cone reamer, the gages, the fine files and stones, lathe, etc) AND the experience, it is not "hard" at all.
If you get really lucky, it can be as simple as simply removing the old barrel, spinning on the new one, and find that it indexes and gages b-c gap correctly. If you are not lucky, (40%-80% of the time), you will need the special tools and skills to properly fit the barre.
That is why we recommend that you have a qualified gunsmith do the work.