Header Image Fill Space

I’ve reviewed other forum questions on how to make my header fill the entire space but, unfortunately, I know absolutely nothing about code or making changes. I certainly don’t want to mess things up – very new at this. I have an image I’ve uploaded that I want to use as my new site’s header. The size on the image is 607×255 but I’m not able to increase the size to fill the entire header portion of my page. Any help, instructions, suggestions are greatly appreciated! The site link is below but it’s very, very new…just started building.

http://nancyharmonorg.ipage.com/wordpress/

Lorri