i think the longer part just snaps in/out. the rear part (aka "sail panel") has a couple nuts hidden behind the interior panel. you have to remove the seat belt at the top to take that panel off. after that, you'll be able to see the nuts holding the sail panel in place.
The piece that goes from the windshield to the back of the door glass has some screws that hold it in too. You have to remove the weather stripping to gain access to those screws from underneath the panel.
The rear piece you can access the screws by removing the interior panels around the rear side glass.