Custom Logo in Header + Resizing

Hi, everyone!

I'm new to the forum, and have a question for y'all.

I am such a newbie, but love this theme and am doing my best to figure out how to customize it to my needs. I'd like to upload a custom logo, that would sit in the upper left sidebar at the very top (to replace the custom header altogether), and then have posts start at the very top of the page, rather than start below the existing custom header. Does this make sense?

Here's the site: www.dreamydish.com

Thanks for any help . . .

j.