Glad to hear it has been helpful and your welcome.
I am not totally understanding what you are wishing to do. Do you mean, similar to my example image (the image above was much smaller than the background image), take the overlaying image (Layer 1) and re-size/re-scale it to the same size as the background image?
If yes, there are two ways to do it. Just a quick answer for now:
(1) One is to take the dimensions of the background image via
Image menu -> Image Size (make a note of the document sizes), then copy the image above (Layer 1) and paste into a new document. Re-size the new document to the same size of the background image dimensions of the main document using the Image menu -> Image Size using the same dimension size as the main document. Then copy-paste back into the main document. (If Constrain Proportions is checked, it will resize in ratio to the original. You can turn the Constrain Proportions off but the image may look a little warped if you do. Depends what kind of image it is, you can get away with it. Or leave a little of the layer overhanging over the edges of the background image.)
(2) The other way is to select the above layer (Layer 1) and go to
Edit menu, choose
Transform -> Scale. This is probably the easiest for you.
Then you will see boxes appear above. x and y for height and width pixel dimensions, and W and H for percentage of increase or decrease (these each start at 100%.) Use either percentage or pixel dimension approach. Pixel dimension will be more accurate if you already know the dimensions of the main document (ie: background image.)
If you would like me to post sample images for doing both of these, I can do it tomorrow. I am up late at moment, not fresh enough to do it I was just passing through. lol
I won't get into technicalities, but in the earlier versions of Photoshop there was a reason I preferred the first option (accuracy of pixel transforming.)
Different types of transforming techniques the best depending on type of image (very simplified & roughly put: black & white, detailed, blocks of colour.)