The service manual says that you have to remove the door trim panel, then remove the bulb from the back side. To remove the panel, there are some hidden screws that must be removed before popping it out. The manual won't let me copy the instructions out to paste here (sorry).
Ah, I was confused also. But, alas, I still don't know how to get the illuminated scuff plate off, sorry. I would think maybe it snaps on? I haven't looked, but are there little indents on the ends/sides that would indicate it's just held on with pressure?
Another thought...I think you can buy similar illuminated sill plates from K5optima. So maybe there are online instructions included you can look up that might give you a clue?