They give you a plastic bag to put over them which helps it slide (I learned this after I struggled for a whole LOL).
You can't remove the old leather because they injected the armrest with foam and it would all come apart so you slide the new ones over the old and it is a really tight fit. After an hour or so of struggling my hands were tired and I'm too old for this stuff.
The seats were not a big deal, I have to do the Denali next and will do headrest covers as well, gonna take headrest and armrests to the upholstery shop.
I'm learning to pick my battles.