Hello,
You need to reduce the size of your logo.
Open your customizer and go to:
Header->Header Logo ,and reduce Logo max-height & Logo Shrinked Max-Height http://prntscr.com/f3mvb6
Regards
Well everything depends on what device screen resolution you are viewing website.
If you shrink your logo to 50px on 1920×1080 (full-hd) screen everything will look ok in one line: http://prntscr.com/f3ntp2
But real solution for you is to rename your menu link names to shorter names or to reduce the number of parent links… this is not theme issue this is too much menu links in menu area issue and you must decide what you will do with it.