Upfront Builder help needed with main area width

How do I change the width of the main area in Upfront Builder? I would like my themes wider than 1080. See what I mean here: https://drive.google.com/a/zendesignfirm.com/file/d/1ao94i0D6xmwhDRC79BGj4tnXaGL_cD3T/view?usp=drivesdk

Thanbks,

Joe