How To Replace The Black Header Background

Hello,
Im using this theme and i really love it!! and the fact of it being very simple, clean, responsive and easily customizable is just amazing!.

But i have only one little problem here now which is that; my client wants me to remove the black background of the header(where the logo sits) and replace the whole of that background with an image of their own choice, so my question is please is there a way i can do this? if this is really possible, im kindly asking for help on how i can go about it.

Hope i will definitely get help from here.
Thanks in advance.