Remove the mirrors and the windshield. Then you have to pull the vents out. This is a little tricky.
Get a very skinny screwdriver... put the edge into the inboard side of the vent. Pry it out by pulling the inboard side out.
Repeat for the other vent.
Then you have to remove the outer body part of the vent. It's held in by 2 latches on the top and 2 latches on the bottom.
You need to release the 2 latches on the top (they are easier) first... then release the 2 on the bottom. Pry out the outer body. Repeat for the other side.
Now, and only now, will you be able to remove the speaker covers.