How do I adjust header spacing, page width dimensions etc

I’m just setting this Aegaeus theme up, and I want to make a few customizations:

1. I’d like to close the white space underneath my logo image on my header on all pages/posts,

2. I’d like to increase the width in pixels of all pages/posts

3. I’d like to eliminate the background space above the header so that my header pretty much butts into the top of the browser window on all P/P’s

My site is here:

http://www.water-tech-animation-plus.com/

I have used CSS before, but on old school html sites and I’m lost trying to do it here in WP. Can you help?