Changing stacking order

Hi there, first time ever on a forum so please forgive me.

I have an FLA with a section in it where I need to swap between images (one over the other and so on, which I have done using swap depth) what I want to know is if there is a way to make the transition from one pic to the other smoother by using alpha from 100% to zero, thus revealing the picture beneath.

Does anybody out there know how this is done.?