Apple Aperture 2 - Manual (Page 517)

Chapter 18 Creating Slideshow Presentations 517
IV
Modifying Slideshow Presets
You can modify slideshow presets to create custom slideshows for any presentation.
To modify an existing preset:
1 Choose Aperture > Presets > Slideshow.
The Slideshow Presets dialog appears.
2 Select the preset you want to modify in the Presets list.
3 Modify the slideshow preset’s settings as appropriate.
4 When you’ve finished modifying the slideshow preset, click OK.