remove a sidebar

In Appearance – Theme Options.
Layout tab.
Change sidebars to hidden.

But that leaves the minimum 150 of white space rather than letting the main content go wider

I added this to the css and it made it wider, but not full page:

#main {
  min-width: 100%;
}

try adding this

#main #content,
#main #footer {
    margin-left: 43px;
    margin-right: 41px;
}
#main #fixed-bg {
    background-position: -11px 0;
}