Attempting to bring images into mockup photo. Can't get rid of first image to bring in second image.

I have an Etsy shop with greeting cards that can be framed.  I am attempting to move several different card images (one at a time) into a mock up frame so that I can post in my listings an example of a particular card in a frame. 

The first example worked fine.  I moved the card into the frame and it worked wonderfully.  But when I deleted that layer and began to try the second card, PSE put the first card back into the frame, even though I had deleted that layer and the original image was not even in PSE anymore.  Somehow, it remembered the first image and did not recognize the image of the second card. 

My process was to select the first card image, then Edit>Paste it into the mockup. How can I get rid of the first card image so that I can place the second, third, fourth cards... into the frame for their individual listings?