JUST FIND AND SWAP THESE CLASSES IN templates/tmpl_yourtemplate/css/top_menu.css

//// Old CSS classes////
.topMenu b span.down img {
    margin-left: 4px;
}



//// New CSS classes////
.topMenu b span.down img {
	width: 16px;
	height: 16px;
    margin: 8px auto 7px auto;

    vertical-align:middle;
}