Hi,
There are couple of ways to solve this issue. 

1. Try to reduce the number of top level menu items
For example, you might not need link to Home, because the logo already links to the homepage.
You could also try to rearange main menu items like adding "contact us" under "About us", etc...

2. You can set the header to full width in theme options:

This will create more space for the header on desktop screens, as the header will not be limited to the grid.

3. Remove letter spacing with custom CSS. You can copy the following CSS snippet to Theme Options -> Custom CSS:

@media (min-width: 992px) {
    .nav-menu .menu-item>a, .nav-menu .menu-item>span {
        letter-spacing: 0!important;
    }
}

This will make the menu items more condensed and change the header from this 

into this:

I hope this helps.
Kind regards,

Andrej