First, remove or at least bypass the front wheelhouse rearmost covers to access the rocker panel forward attachment screws. Same for the rear wheelhouse.
At the base of the door sill is a front to back black seal, grab it at either end and pull it from it's channel. This will expose the multiple screws behind.
Lastly, the sill cap is to be removed (the threshold thing that says Mercedes Benz). Access screws are just inboard of the sill and covered by caps. After removal of the sill cap attachments, gently pry up the sill cap. The sill cap is slightly fragile as it is made of plastic, so be careful as you detach it from it's channel.
Aside, from the obvious rocker panel screws, the rocker should be free of the body now.