Hi HelenT,
What you can use is the Override function -- in the Override Settings window you will find a section which contains the Auto Forward settings (including the delay, slide duration, etc.).
Simply turn Override ON and set the necessary Auto Forward settings inside the Override Settings window and these will be applied to all your lessons instantly.
For details on how to use Override, please have a look at this article:
http://support.brillkids.com/entries/20608263-how-to-change-playback-settings-for-all-little-math-lessons