I am having trouble changing the length and location of audio (music) files in my slideshow.  When I select the beginning or end of an audio file (by putting my cursor at the two sided arrow) and try to shorten it, it doesn't seem to move left or right. Actually sometimes it appears to when no audio file is immediately next otherwise not.  Also, how can I grab a particular audio file and move it somewhere else in the slideshow between two other audio files?