This worked for me:
$(".ProductList li:first-child img")
.mouseover(function() {
$(this).attr("src", "http://cdn2.bigcommerce.com/n-pktq5q/b2aus7wd/products/88/images/460/cmpltunknwn_wolfgold_view003__18141.1396558339.1280.1280.jpg?c=1");
})
.mouseout(function() {
$(this).attr("src", "http://cdn2.bigcommerce.com/n-pktq5q/b2aus7wd/products/88/images/461/cmpltunknwn_wolfgold_view001__55714.1396558344.330.330.jpg?c=1");
});