Headway fluid-HEIGHT wrapper

I don’t know CSS, but I’ve done a pretty decent job building everything I needed on Headway without knowing it. The problem is on a 27in iMac my site looked totally different!! the 550px backgrounds that fill my laptop screen look chopped on such a large screen so I need to make them a fluid height somehow. The content in the wrapper that has the large images is actually a text box with a fixed height of 550 (that I want to be fluid now). ANY help is appreciated!!

http://www.SamanthaRubyPhoto.com/musicphotography

Thanks thanks thanks