how do I re-size thumbnails in (add photo) print mode

[tusteplady]

When I print my photos, I like to print 8 wallets to a page. I highlight/double click on the photo - select file - print, which brings up the print photo box/screen, then I select - +add, which brings up another box/screen - organizer. These are the thumbnails I select from to add to print photos box. How do I make those thumbnails larger, they are about an inch square. Sorry for my lingo, I am a true beginner.