An easier way would be to edit the header.php of your theme. Make a copy of the file from the parent to your child folder before editing.
Move
<nav id="site-navigation" class="main-navigation" role="navigation">
...........
</nav><!-- #site-navigation -->
to just before </header><!-- #masthead -->
Had used the same on my site after finding the solution here at support itself.
Hope it helps.
Hope it helps.
Cheers.
