Change the slide size
1. Select one or more slides in the slide list area.
2. Choose in the group Size, you can choose:
Scale 1:1: It means that image will be initially displayed centered on screen using its original dimension (scale 1:1).
Maximized: It means that image will be displayed maximized on screen.
If you specified a Margin in general tab, the image will not touch the border of the screen.