Remove all the screws you can see under the armrest when its open. dont' forget the one down near the hinge in the back.
The plastic that you just took the screws out of will separate from the top (the sliding part).
Then you'll see four screws that hold the pad to the sliding part. You have to slide the pad to align the screws with some holes for access. Once you get into it, it'll be obvious.
Its not difficult at all. I did mine two weeks ago to put new vinyl on it.