Can't find the onrelease function

I am new to flash. I downloaded the image gallery and am looking to pick it apart to learn some stuff. I understand the functions, nextimage and previousimage, but I don’t see where they are being called. I looked at the buttons, and see no scripts associated to them. Can somebody give me a step by step on how to see this?

My goal is to use this to build a similar image gallery, but with thumbnails. When the thumbnail is clicked, it will load the image from the xml. I know I have to probably write a new function and call the number of the array that needs loaded. I am just trying to take baby steps.