IPhoto Files

How do I find/delete all iPhoto files? Please excuse my ignorance here, I'm strictly a Photoshop user.... Recently my wife has been working on a slideshow for her school, it started with nearly 2,000 pictures before she trimmed it down to the current 500. I thinking that over the course of this project that my poor MBP has been kind of chocked full of pictures. I do know that iPhoto doesn't like to delete files, but don't remember just how to get rid of them.