I've fitter some airvent surrounds myself. I didn't have too much trouble removing the old ones. I used a pair of stubby-nosed pliers.
the way I did it was focusing on the top of the airvent were the most plastic surround is exposed.
On the Top of the airvent, gently push back the dash (its soft, use something plastic and broad, like a spatula or a ruler)
Grab the top of the airvent surround with the pliers, careful not to grab the fins inside the vent.
Hook one of the pliers front teeth over the edge of the plastic surround (ie so you dont lose grip). This is why you're pushing the dash back, to expose the back of the airvent surround. You want to get your pliers front teeth hooked over the edge.
Pull quite firmly with the pliers, moving slightly left to right
and presto! the airvent surround pops out! (at least mine did)
I had to try a few times, as I lost grip with the pliers. But it required quite a hard pull.