How to change a LibreOffice Impress presentation from 4:3 to 16:9 ratio?

For Version LibreOffice 5.1.2.2. - Select menu option "Slide" - Select "page/slides properties.." - Select folder "Page" and "Paper format" options.

For LibreOffice up to version 4.x:

1. Click Format
2. Select Page
3. Click Screen
4. Scroll through the various screen sizes until you see one that matches your criteria.

Annoying but true. Changed in LibreOffice > 5.0. Go to:

-> slide -> Page Slide Properties

and then adjust. Just took me half an hour to find this menu item. It sucks because official documentation is not updated and finding specific items in menus and submenus can take you a long time.