Welcome to the forums Francis,
I don't have a definitive answer, but I think my guess will be fairly accurate. I don't think you can. If you created your slide-show using PSPP, you're actually using the Project Creator
that is included with it. It is very basic, and limits you on what you can do. I won't even get into the problems, hair-loss, shattered nerves you may well experience with Digital Studio 2010. Corel just flat dropped the ball with that one. In order to provide any sort of meaningful help, I, probably most others, must regretfully fire up the program to see if we can figure out an answer. It's just a program we refuse to use.
Have you had the program for more than 30 days? If not Corel does have a 30-day money back guarantee..