How to lock the place where images land when dragged?

Hello,

How can I do this:

I have multiple files for the same picture, Eg: File1_Rev1.psd, File1_Rev2.psd, etc.

When I open the lates Rev and try to drag an earlier version of the same file on top of it, for some reason it puts it in a random place, I'd like the image to land exactly on top of the one already there.

How can I do that without moving the pointer exactly to the middle of the picture?

Pardon me if this is something basic, but I don't work with pictures, I'm just an IT guy.

Thanks.