I did this already in my car. Just go ahead and get a flat tipped screw driver and insert it between the vent and the dash, then pull the vent out by moving the screwdriver up and down like a lever, this should give the vent a bit of slack so it pops out.
If you need any more help, I'll gladly post a video on how to do it.
The ones in the dash pad are easily removed by inserting a small flatblade between the thumbwheel and prying outward to release the pin. The ones in the instrument panel CANNOT be removed this way. You must remove the instrument panel first as they are fixed from behind.