I am showing used space with the files on my MacBook Air (SSD). How do I get rid of that without losing everything?

I have a MacBook Air 13" with a 120GB Apple SSD TS128E. When I go to "Storage" it says that I have 38+ GB of movies but there are not any movies on my computer. I can't do a "Erase Free Space" because it is a SSD. How do I get rid of all this "ghost" data without losing all the other apps, including Parallels and Windows 8, on my MacBook?