Change Header Image?

I tried to submit this question earlier, but I don't see it anywhere on the forum. When I attempt to change the default image in the header by adding my own image, I end up with my own image on top of the default image. How can I make my image the background image instead of a layer? 

To clarify, do you want to remove this image and replace with your own image (see my screenshot below)?

Please provide us with further details of your requirement so we can provide you with a detailed answer and solution.