HI
You can hide it by CSS:
.t3-header .t3-megamenu {display: none;}
In case that you want to move the code which render this menu, you open the file:
/templates/ja_directory/tpls/blocks/header.php
and remove lines 91-93:
<div class="t3-navbar navbar-collapse collapse">
<jdoc:include type="<?php echo $this->getParam('navigation_type', 'megamenu') ?>" name="<?php echo $this->getParam('mm_type', 'mainmenu') ?>" />
</div>