I've removed mine. But they are held on by those tabs that you see from the fascia going through the actual black plastic cover. Behind the cover there is a metal wedge-like piece that slides down into the tab to hold the cover on.
Here is a great mod for the lower vents that GMACJR65 just posted, which has a clear picture of the back -
http://www.300cforums.com/forums/ext...-me-grill.html
After removing mine and removing the air silencer, I "feel" like I am getting more air to the engine. I'm lucky I saved my covers as I am now going with the mesh down there to match my grill with the help of GMACJR65.
Good luck.
EDIT: Just realized you have a '10 SRT - might not be the exact same. Sorry.