Gap between menu bar and text on page is too big. Help?

Hi there
I’m using TwentyEleven and the gap between the upper menu and the text on each page is too big. (image attached below)
Can anyone advise how I reduce this wasted space please?

Thanks

https://dl.dropboxusercontent.com/u/13335648/too-much-gap-wordpress-menu-to-text-on-page.jpg