Resizing Storyline files

Hi All, 

Background, we have a series of templates created in 5:3 (950x570) aspect ratio. We have since realised this is less than ideal for software sims etc. So all I wanted to do was change the templates to 16:9.

However, I have tried the various options in Story size setup and I just cannot get a project to resize correctly. The original slide content remains at the original dimensions and the background page gets larger.

Am I am being daft? or is the resizing of each element a manual task?

Any help would be hugely appreciated.