What's new in PowerPoint 2013-3 - Aspect ratio, change from 16x9 to 4x3

If you want to change the default aspect ratio for a new presentation to 4x3 here's what you have to do:

Start a presentation based on one of the themes.

Go to the Design tab and in the Customize group click the Slide size button.

Choose the 4x3 ratio.

In the following dialog choose between Maximize (slide content may appear enlarged) or Ensure fit (slide content may appear smaller).
Note that the dialog will not appear if you have chosen the blank presentation theme.

Choose whatever fits you.