Depending on the model year and body type of attachment may vary.
Front bumper
The bumper is fixed very simply. Unscrew the two screws under the number plate, take out the caps in the lower part (if any) and Unscrew the screws that attach the fender liner. Then pulls the bumper with the rails in the wings forward.
Rear bumper
Attached is very simple, the attachment points indicated by arrows.
How to remove front and rear bumper Mercedes Sprinter 2 (after 2006)