you wont if you - it's fiddley but these helped me when I did mine- PVR's pic shows you where to push ;
http://www.z4-forum.com/forum/viewtopic.php?f=12&t=474&p=6994&hilit=removing+vent#p6994
Video is helpful to see it in action;
http://www.youtube.com/watch?v=QRfemGE-kY4
It's easy when you have done it once but takes time the first time- be patient and careful and you will have no need for new vents mate.
If you cant see the tabs, point the vents down as far as they will go, push 2 small shafted screwdrivers up through the vents from the 2nd or 3rd gap from the top and aimed at the nearest part of the slots to you, then lever the screwdrivers towards you.