Unscrew these two tri-wing screws holding the backplate in place.

The other screws keep the PCB and the plastic frame together, it's not necessary to unscrew these for outer shell replacement.

Start to lift out the backplate near the top-right corner, and then you can gently wiggle it up and off.

When putting the new backplate back on, make sure that the bottom-right corner is flush with the plastic frame. If it isn't, lift out the entire backplate, and try lowering it again, but try gently pinching the plastic frame and the backplate together, like shown on the 3rd image. Do not try forcing it into place, it will not work!