Customise Vintage Prints Slide show

Hi,

I've tried to make a slide show with the Aperture 3.4.5 and I liked the Vintage Prints theme. The only problem is, how can I decide if one or two pictures are displayed on a slide. I've tried to find an answer on the web, the only partial answer I found was this: https://discussions.apple.com/thread/2678967?start=0&tstart=0 but I didn't manage to apply the solution.

Thanks in advance for your help.

Cheers,

Sharlo