How to make pages fill the screen

I am using this theme as a website , not a blog. I have a home page. Then I have another page. when I go to the other page the header and sidebars remain in the same place and the new page appears in the middle bit. How can I make the header and sidebars disappear and just have the page contents? I have tried changing through all the page type options but none of them make any difference at all.