Problem Displaying "Header Image"

Hello, I love the theme, thank you. I would like to put a logo on my site in place of “Site Title and Tagline”, however when I upload an image, it is huge.

No matter what logo I upload it’s stretched out and bleeding over the menu bar. I just want a logo of the site name on my site to the left of “Intro” on the menu bar.

How can I achieve this? I’ve tried resizing my pics with no luck, please advise.

Site:
publishmymom.com

Thank you,
Matt