Sets.

How on earth do you make changes to a set of images, as a whole, on Adobe Photoshop (7)?

For example, I have around 25 frames that are going to be made into a Gif. I want to erase the edges of that GIF, but in order to do so, I have to click each and individual frame to do so. If I click the set and try to erase or do something, it tells me that I'm not able to do so.

The only thing I CAN do as a set is change the size of it.

Thanks!