Hello,
Easiest way would be to adjust these padding values until it is near the center. Then you can make custom @mediascreen calls for each device resolution with overrides and changes for those resolutions. There are already a bunch of these in place in the s5_responsive.css file.
Template.CSS - Line 329
#s5_inner_padding, #s5_header_area_inner, #s5_logo_wrap {
padding-left: 10%;
padding-right: 10%;
}