For the center air vent:
1. Open the passenger side storage, remove a screw on the right of the center air vent.
2. Use an Allen wrench, loose the screw inside the vent ( this bolt connects the lever to the door inside the vent), just disconnect the lever from the door, the lever will hold the screw, you don't need to remove the screw.
3. lift the right edge of the air vent by 1 cm, then use two small flat screw drives to lift the two hidden clips in the left vent by 1 cm, then lift the right edge further more, the air vent will come out.
Installation is the reverse of the removal, the most difficult part is to re-attach the lever to the door inside the vent, you need to hold Allen wrench by one hand and adjust air vent lever by other, until the screw bites, then fasten the screw to allow lever to be able to reach max open position.
Feel the vent, you will realize why MBs are so heavy.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.