This theme is built using the bootstrap css grid, which allows for easy modification/customization of the template files. Each row is comprised of one or more divs of the span# class where the total # is equal to 12. The header, for example is a span6 followed by another span6. To change the width so that the Site Name area is wider than the Slogan area, you would change the first span6 to something larger like span8 and then change the Slogan area to whatever adds up to 12, in this case span4. This same technique could be used to modify the width of each area in each row of every page type to fit your individual needs.