You first have to remove the stereo. To do this you have to open the two small flaps on the sides and then use the factory tool or a small allen wrench and twist until the catches release and allow you to slide the deck forward. Looking up you see two screws going up into the bottom of the vent. Remove these.
Pull the bottom out and then slide downward to release the plastic clip holding on the upper left corner.
You will not be able to remove it at this point. There is a cable attached to the back of the left most dial that controls the bias in temperature between feet and face vents. In order to release this cable you will need to remove the lower driver’s side knee panel and the heat shield beneath it. Once you do this if you look towards the center of the car on the side of the central plastic core to the ventilation system you will see a blue cable with a yellow end.
You have to release it in two places. The first is at the bottom of the cable on the side of the heater core vents. It is a black plastic hoop that is snapped over top the white nub that looks like it is split in two. You will see this at the center of the picture
The second place is at the yellow portion of the cable. It is snapped into a black catch on the side of the ventilation chamber. In these last three pictures down is to the right.
Removed, the complete assembly looks like this:
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