Removing color overlay and gradient on homepage

Hi!

I wold love some help/assistance/tips from you guys! I am making a website with the lovely hitchcock theme, but my client would like take out the color overlay/gradient and just have a picture for a background that can scroll along. Is this possible? And if so, how?! I managed to take away the gradient en have just the picture, but the bottom half is still a grey color…

Thanks in advance! Hope to hear back soon ??

Nikki