Make lifestyle theme fit accross page

Hi

currently my website seems to be just centred in the middle of the internet page with margins down the side and I am only able to add so many menu items before it puts them onto two lines.

Is there a way to make it so that the theme takes up the whole of the browser window with no margins so that I can move my logo and menu accross to the left of the window.

Hope this makes some sort of sense any help is appreciated