Depends on how easy it is to access. If you can get to it without removing stuff, they are really easy to replace. You loosen up a bolt and unplug the connection, and it comes right out. The replacement goes in the opposite way. The only remotely tricky part is making sure you get the belt tension right when you put the new one in, but even that is straight-forward.
When I changed one in an old Camry, it was a little more work because the replacement was exactly the same except it was missing a cut-out to accommodate a bit of metal that stuck out on the mount on the engine. I had to file off the metal, which was a bit nerve-wracking, but it worked perfectly once I got it in there.