I haven't done mine yet but on the V6, I'm pretty sure you can't change the primary one from the top. It is on the bottom, near the middle front. Find the cat converter and this is right before it. The wire clips looks a bit tough to get out for this one because it is up in the cavity.
The inline 4 might be from the top.
How easy really depends on how rusted to the pipes they are. PB blaster or Kroil might help.
I have 124000 miles and I can tell you I will do them myself when the time comes but now is not the time. I can only imagine how tight they might be haha.