Thanks much, Splinter Cell, for the pic with the metal tabs. I was able to remove my vents today.
The passenger side is super easy, just keep the glove compartment door half-open with your knee and your hand can freely access the vent. It's easy to feel the metal tabs and push on them. I pushed one side first, then wedged it with a coin to prevent it from going back in, then the other side.
The driver side is trickier. Unless Splinter Cell posts instruction on removing the storage and buttons panels, I got lazy and went directly for the vent instead. I lay down on the carpet, my head touching the brake pedal, my back is on the side step (perhaps a pillow on the carpet might be easier on your back). From that angle, I can clearly see the vent with its two metal tabs, and was able to push them with a long screw driver. However, this side is a little harder to pull out, I had to hold the tab (that change air direction) in the middle of the vent and pull it strongly.
In the pictures below, you can see that the chrome trim can be removed independently of the black window below it. I wasn't sure which latch is which, so I detached the whole window first before removing the chrome trim.
Again, thank Splinter Cell for your pointer. It's just a matter of spraying PlasticDip now.