length (time) of slideshow frames won't change -- it stays at "7" even when I change it in "properties

I'm trying to make a slideshow, with embedded music. I dragged and dropped each of the 54 frames into proper order. I loaded the music. When I played the result the music (4:35) played for the proper amount of time, but the pictures took over 6 minutes to play. I read the tutorial (it did't mention how to change the picture display from the default 7 seconds to 5 seconds) and I watched the You Tube tutorial (https://www.youtube.com/watch?v=FWqH5dBwdKI) -- the oversized letters layed over the original smaller letters made it impossible to read either one, and the music increased my agitation. The instructions about clicking "control" were confusing. How can I make the slideshow last 4:35, the length of the music? Also, how can I make one of the frames 10 seconds instead of 5 seconds? thanks