每次图像更改时UIImageView分配内存 - 如何发布？

I'm trying to create an application that allows users to go through a set of images like a magazine. I've got one UIView class on top of the AppDelegate and on swipe to the left/right I'm either going forward or backward a page. My problem is that when I swipe and change the image source the program keeps allocating more memory, and I'm not certain where/how to release the previously allocated memory. I've looked in to the difference between imageNamed and imageWithContentsOfFile and I believe I'm using those correctly so I'm stumped. Any help would be much appreciated!I'm trying to create an application that allows