To remove the plastic pins, you have to push down on the center "bullseye" and then lift up on the edge of the pin. If you don't push the bullseye first, you will break a few pins. You will probably need to remove about 2/3rds of themstarting on the passenger side.
The AC filter looks like an engine air filter. It is under a flap which is under the passenger side of the black plastic cowl that runs across the firewall. The flap is snapped in place so just pull the front edges forward a bit and up. The filter should slide right out and is quite easy to replace.
If I recall right to reset the message you have to push in and hold the reset button til it beeps at you.
I actually just blew my filter out with compressed air.
Good Luck,
Jim Henderson