You can remove this property::
#ja-mainnav ul li span.menu-desc, #ja-subnav ul li span.menu-desc {typo.css (line 30)
display: none; >>> remove
}
To make it look nice with description on, You can decrease font-size value accordingly::
.ja-megamenu ul.level0 li.mega span.menu-desc {mega.css (line 53)
display: block;
font-size: 92%;
font-weight: normal;
}
and even increase the graphics height ::
.ja-megamenu ul.level0 li.mega.active a.mega, .ja-megamenu ul.level0 li.mega.active a.mega:hover, .ja-megamenu ul.level0 li.mega.active a.mega:active, .ja-megamenu ul.level0 li.mega.active a.mega:focus {mega.css (line 49)
background: url(“../../images/mainnav-active-r.png”) no-repeat scroll right 3px transparent;
color: #333333;
}
and
.ja-megamenu ul.level0 li.mega.active {mega.css (line 45)
background: url(“../../images/mainnav-active-l.png”) no-repeat scroll left 3px transparent;
}
Source psd file for above graphic elements :: can be found in source files of specific template