To take the skimmer off, you just take all of the screws out of the faceplate. That is all that is holding it on.
To take your return off, remove the backing nut on the outside and push it into the pool.
This video is how I installed mine - sort of
I used what they call the wall saver (or butterfly) gasket.
I did it a little differently. I first mounted my skimmer and faceplate temporally
Then I cut the liner, leaving about two inches of material all around the opening
I cut the corners on a 45
I then removed the skimmer and faceplate.
I folded the two inch flaps of liner that I made over the opening and taped them down at the edges outside the pool
I then installed the butterfly gasket
Then lined up the skimmer and faceplate with the opening and installed the screws.
I then trimmed any excess liner from around the outside of the skimmer (on the outside of the pool)
Basically, they cut the liner flush with the skimmer opening. I left enough material that I could fold it over the edges of the opening.
I really don't know if it makes it better, but in my mind it can't hurt, and it is an extra layer of protection.