Xcode 8 beta - How do you change the size of all the viewcontrollers in storyboard?

Question

I was previously using xcode 7.3 and just upgraded to xcode 8 beta but in the process the sizes of all my viewcontrollers on storyboard went from a wider (iphone 6 plus type of size) to a narrower (iphone 6 type of size). This has really messed with my constraints and I was wondering how do I change the size back? Any help would be greatly appreciated.

Below is the picture of the current view controller size in Xcode 8 beta

Answer 1

As of XCode 8, at the bottom right, select View As: (and then the device you want)

Answer 2

From here you can set/select all the screen sizes available