amaurice
Hi
Your header already has too much items if you increase logo space you have to make the menu item in 2 lines.
At the moment you can open template folder /tpls/blocks/header.php file
and change the col-lg-8 to col-lg-9
so the Menu container have more size. Now decrease the right header position size from col-lg-3 to col-lg-2
example http://prntscr.com/12lou3d
To make logo bigger you need to increase the logo col-lg-1 size to more.
But make sure total size of columns will be 12.
If logo use col-lg-2, Menu col-lg-8 and right head position col-lg-2 = 12
In this case menu again split in 2 rows.
Only way is put the header full width by adding this code in custom css
.t3-header.container {width:100%}