Mercedes-Benz 2005 E -Class Wagon Operator's Manual page 265

Controls in detail
Useful features
Removing cup holder
1 Cup holder
2 Locking pins
Move both locking pins 2 in direction
of arrow.
Take cup holder out upward.
264
Reinstalling cup holder
3 Locking pins
Insert cup holder.
Move both locking pins 3 in direction
of arrow.
Rear cup holder
Briefly press the front of the armrest.
The cup holder extends automatically.