My site has a total width of 1050px (appearance > parabola settings > layout settings) but I can not see where to change that setting. I would like the sidebar width to stay the same (250px) but the total site width to increase to something like 1274px (1024px + 250px).
The theme’s layout and widths are configurable on the theme’s settings page, under Appearance > Parabola Settings. Note that you the theme requires the companion Serious Settings plugin to activate the settings page.