setting aspect ratio

Kind of a noob question here. 🙂

I just got a used Panasonic AG-AF100 as my first professional camera. How do I set the aspect ratio to shoot in? Say I want to shoot in 2.39:1. I don’t see a way of setting the aspect ratio other than 16×9. Or do I just use the aspect ratio marker display (it will show a 2.39:1 safety zone on my lcd and monitor) as a guide and then “crop” it in my post production software?