I think you mean to address the widths at which things change? Go through all the files in /css folder with the word "responsive" in them. You'll find where you could adjust the widths at which items are transformedfor tablets, phones, desktop...
Also, you can of course create your own breakpoints for specific things and transform them with your own CSS at the end of custom.css...
In variables.scss, you see things like this:
// Navbar
// -------------------------
$navbarCollapseWidth: 979px !default;
$navbarCollapseDesktopWidth: $navbarCollapseWidth + 1;
and that variable shows up later in _responsive-navbar.scss :
// TABLETS AND BELOW
// -----------------
@media (max-width: $navbarCollapseWidth) {
Not sure if this is helpful...
