Edit video aspect ratio

I have a Samsung UE65ES80909 Smart TV. I'm trying to watch a film with a 1.66:1 aspect ratio. The aspect ratio comes up automatically as 1.85:1 (16:9). I would like to change it to 4:3 so that I can see the full image and have black bars on all four sides, but the menu option Picture/Screen Adjustment is not available. Why? How can I enable this menu option?

Thanks,

Andrew