changing header and banner

Ten years ago a friend set up a blog web site for me. I’ve enjoyed blogging but never liked the heading at the top of the page. The friend isn’t available to redesign, so I want to do it myself.

I have a design done in photoshop (1000 X 375 pixels) with some text on an image that I want to use and wondering where to go in my dashboard to begin.

I need step by step advice in simple terms as I don’t have much experience in this realm.

Thanks in advance for any help.

The page I need help with: [log in to see the link]