Limit Posts on Homepage

I am using this Theme on my Site Geek’s Top Ten but there is a Problem I am facing, I want to limit the Width of Whole blog to 1024 pixels and show both sidebrs, but the Problem I am facing is that there are two posts side-by-side on homepage’s Main Stream, I want them to Make only one post in main stream, can you please help me in this?
at the time I have Hidden secondary sidebar.