There are two clips built into the bottom of the vent opening pressing down towards the top of the NAV unit. These are located 4 slots from the left and right, respectively. Insert a very small, flat bladed screwdriver into the center bottom slot of the vent. You will see the clip or retainer in the lower surface the vent. Insert the screwdriver into the edge of the clip and lift slightly. Now gently pull w/ wiggle the vent outward. Repeat on the other clip until the vent is free.
I documented this in this article -
http://www.xoutpost.com/articles.php?...ticle&artid=94
