Adding a header to Hueman 1.5.3

I’m more of a plug-and-play guy, so my level of frustration/confusion is pretty high right now. I had to move to a new theme when my old one was updated and changed completely. I like what I’m working with, but would prefer to replace the solid color-block header with something more dynamic.

For reference, the site is https://www.cubsinsider.com

To that end, I have two questions:
1) How can I replace that header with an image that stretches across the whole screen? Not the entire background, mind you, just the header portion.

2) How can I center the logo image I already have?

Thanks!