Sending images to the back when clicked

okay cleaver people i need your help again :azn:
basically im making an image gallery this is what ive done so far
imported all of my images that i wanted to use and converted them to movie clips
ive put these movie clips in another movie clip which is masked with an instance name of master_mc

the images are placed on top of each other so it looks like a stack of photos
what i want to do is when the user clicks the image on the top it should send it to the back of the stack of images and continue to do this for all photos.

please help me i need to do this for my work

and btw i need to do this in flash 8