Hi there, well I've got version 9 here, but typically, the related files should not be deleted, because the internal files of the program are all there to enable you to edit NON-destructively. They are only container files, holding info covering where actual video, picture, audio files are located, effects added etc, but NOT actual media files.

You should be able to delete slideshows within the program, under File? Cheers, M o' L.