How to increase content width in twenty thirteen theme

Hello

First of all wordpress have very good theme twenty thirteen , Thanks for this.

I have installed twenty thirteen over here

As you can see there is static page showing on front page which will be my landing page.There is space both at left and right hand side , in the middle there is content.

I want content to take more space and on left and right there should be less space..

I know we can do this from css file but I dont know which class to edit…

Can you please tell me how to make that changes ?

Thanks