Slides are automatically resizing upon launch

This is a frequent situation encountered while dealing with content that was initially created for a preview on a widescreen TV where usually the 16:9 format is used whereas most of the devices have aspect ratio less than 16:9 such as iPad has 4:3 aspect ratio.

Changing the slide size is pretty straightforward: 

 In PowerPoint just go to Design → Slide Size → 4:3

Be careful, the slide size change might have other implications on your overall layout and potentially move text boxes/images and other objects as you change the format of the slide.