I am assuming that you don't have the Mercedes hooks to remove it.
This is what you do:
1. Remove driver's side tweeter on dash above AC vent (be careful not to crack it it tilts to one side and then pull out) Unhook tweeter wire (the connection is inside the small foam tube)
2. Under it you'll see two small screw that hold AC vent remove them
3. Now look at bottom of AC vent (inside where the blow direction indicator is you'll see two small clips sticking out left and right. There is just enough room to put a small flat tip screw driver. You have to lift both and pull AC vent out. You can do one by one.
4. Now there should be enough room for you to stick your hand behind the cluster and push out
That's it, just be careful with the tweeter they get fragile from the sun.