Change Page Width in Simple Catch Theme?

Can anyone help me to change this page’s page width?
I have the page set without the sidebar, What can I do to increase the width just for added pages without effecting the width of the main page and forcing the sidebar on it to the bottom?

[closed as duplicate – please start only one topic per problem – continue with http://wordpress.org/support/topic/simple-catch-change-page-width?replies=1 ]