If you have knowledge of CSS you may be able to add and modify the following CSS rule to templates stylesheet.
It may need to be adjusted to fit your templates requirements, use at your own risk, no free support will be provided for issues around this.
/*CUSTOM ARROW*/
#menu #nav > li > a.dropdown-toggle:after{
content:" ";
border: solid black;
border: solid [WSCOL_MENU_TEXT];
border-width: 0 2px 2px 0;
display: inline-block;
padding: 2px;
transform: rotate(45deg);
margin: 5px 0 3px 4px;
}