When you work in normal view on the Slides tab, each slide is displayed as a thumbnail-sized image. You can increase or decrease the size of these slide thumbnail images by doing the following:

1. Switch to Normal view (click Normal from the View menu).
2. Select the Slides tab to display the thumbnail images.
3. Click one of the thumbnails.
4. From the toolbar, use the drop down arrow beside the zoom option to increase or decrease the size of the images.

Keep in mind that the change will apply to all slides in the presentation.