Now that the back is unscrewed, flip the keyboard back facing up. Removing the pad is moderately difficult and needs quite a bit of force as the pad is held down by a lot of tight clips and you may end up breaking a few.

See photo. The panel slides in from the top using nubs and the clips are all along the bottom that need to be forcefully pulled out. Can try using a spudger to loosen the clips - there are 16 that run along the bottom and sides