Organizer Slideshow How to remove audio.

I have created a slideshow with default music. I can select the music note with the plus mark to add additional music. But I can not figure how to remove music from the selection. My first attempt to copy music from the iTunes resulted in the music upload but Organizer said the m4a file is corrupt. I change the encoder but Organizer will not allow the new file because there is already a file with the same name.