Header Image upload

Hi, I am trying very hard to design my own site using WP and the WP theme I bought. However, I am having a problem uploading the bkgrd image for the Header. It allows me to “upload the image” but it never actually changes when going to my website, it has stayed with just the color bkgrd. When I go to the “Header” section, I can see my image in there saved as well as the image is saving under “media”. Would someone PLEASE be able to help me with getting the image over to the bkgd of the Header, or possibly know what might be the issue? Thanks SO much!