Width of content in standartemplate

Hi there,
Makeing a new page, based on the standardtemplate, the content-area on a desktop PC with standard Browser is approx. 55% of the width of the screen (1920x1080 pixel). See: http://www.data1.ch/wpalcona/seiten-template-1/
How can I enlarge this up to, say 65-70% ?

Checking your samples, the content part is approx. 60%: www.athemes.com/sydney-pro-demos/ or www.demo.athemes.com/sp-style-2/

Thanks for your help.
Cheers, Paul

Hello Paul,

You are using Front Page template on this page:

Do you still need help?

Kind Regards, Roman.