Open the door, and look inside the open space behind the fender. You'll see an (8mm?) bolt holding the lower end of the exterior A pillar trim in place. It's a bit of a pain in the ass to access, I recommend an 8mm ratcheting wrench.
You need to pull down the weatherstripping in the door frame to access the rest of the screws. There's some screws that hold the weatherstripping channel on, and then you can access the A pillar trim screws.
Hint: when it comes time to remove, the trailing edge of the A pillar trim has a tab that SLIDES INTO the C pillar trim. It does not snap into the C pillar trim. That tab can be easy to snap. I believe it slides down.
Edit: here is a vid
Double Edit: Here is a pic of the back of a spare A pillar I have.
That trailing edge definitely needs to be pulled down toward the ground before you just try to pry it off.