To access the Page Layout settings go to Flotheme -> Theme Options ->Layouts tab.

The Layouts section allows you to adjust the Website Header Navigation, Page width, Image gaps (white space between images) for Blog Posts or Galleries, Blog & Gallery listings Layouts, Layouts inside a Gallery and Video page settings.

You also have the option to choose the Horizontal Layout Height for the Galleries area.

After editing the settings, do not forget to click Save Options button to save the changes to your website.