that piece pulls down. make sure you're not pulling it straight out or side to side or twisting it. just gently pull it down towards the floor.
edit... are you talking about the center pillar? or the rear sail piece that has two clips.. if you are talking about the rear sail try this, it says the piece has to be removed from the outside:
https://i.gyazo.com/d3fdb5609ac2541134363d99efb30f8e.png