Site width

Hi

I have a ProPhoto WP site which can be found here – http://www.mattselbyphotography.co.uk/

the site is 980 px wide but I’m wondering how easy it would be to make the site full width (like the masthead) as its a photography website, I think having images appear full screen would have a great impact on the viewer. My only concern is how much disruption this will make to my site, especially as the images i’ve uploaded to date are resized to 980px wide.