Hi,
Thanks for contacting us and choosing our product!
about problem your, you want change size. Please go to file assets/css/style.css on line 609
Note: you should write CSS via config Custom CSS(Tab Advanced module JUX CSS3 Mega Menu). because when you update version new. those changes will not take. Thanks
#jux_megamenucss3 .megamenu ul.level0 li.megacss3 span.menu-title{
font-size: 12px;
}