in your stylesheet “style.css” (or one of them :P) open the file in your html editor and press CTRL+F and search for “.sub-menu” (without the quotes).
you should see something like this below . . .
.sub-menu {position:relative; z-index:9999 !important}
replace with this
.sub-menu {position:relative; top:0px; left:0px; right:0px; bottom:0px; z-index:9999 !important}
then play with the top, left right and bottom numbers to get the place you want.