After you create a slideshow, you can change its theme (design) at any time.
If you’re in full-screen view, exit it by clicking Full Screen in the toolbar. If you’re using Mac OS X v10.7 or later, move your pointer to the top of the screen, and then click the Full Screen button that appears in the top-right corner.
To change a slideshow’s theme:
Do one of the following:
Select the slideshow in the Source list, and then click the Themes button in the toolbar.
While the slideshow is playing, move your pointer to make the slideshow controls appear, and then click the Themes button:
To select a theme, click one of the thumbnails.
To preview a theme, move your pointer over its thumbnail.
Tip: If you use Places to add location information to your photos, you can use the Places theme, which shows maps and the place names of where your photos were taken. You can also change the place names that appear in the slideshow. Select any of the thumbnail images for title slides in the photo browser (they’re black with a T in the center), and then double-click the place name text and type a new place name.