Then, copy the selection you just made, and paste it. This will create a new layer.
Switch to the move tool like indicated...if there is a duplicate image at the top...use the crop tool and select what you would like to eliminate...then press enter, and that part of the picture will be deleted.
Then all that's left is to use your arrow keys and move the new layer you just made downwards. You can also use your mouse and drag the layer of course.