Enlarge preview pane window in OS X Mission Control
Make a window in Mission Control preview larger
Here's how you can enlarge a preview pane window in OS X Mission Control. This makes it much easier to see what's in the window.
1. Open Mission Control by swiping up with three or four fingers.
2. Put your cursor over the window.
3. Hit the spacebar.
4. You'll see the window expand into a larger view.
Read more: CNet