How do you fill a designed image in PhotoShop?

I am trying to fill a designed image in Photoshop. It currently has a greyer-white coloring and I need to change it to pure white to help it coordinate with a landing page design. I know how to select most of the design with the Quick Selection Tool, but when I go to fill it I am not sure if I am doing it right. I also cannot select the whole design with the Selection tool. When I go to unselect the part that I filled and select another piece of it I cannot get it to unselect the first piece of the design.

I know this is pretty simple, I am just stuck. Any Photoshop advice on what I am doing wrong or another way to accomplish this would be much appreciated.
image-in-photoshop.JPG
designed-image.JPG