function changeMenu(which) {
    var one = document.getElementById('byproduct');
    var two = document.getElementById('bybrand');
    var three = document.getElementById('product');
    var four = document.getElementById('brand');
    if (which==0) {
        one.style.display="block";
        two.style.display="none";
        three.className="selected";
        four.className="";
    } else {
        one.style.display="none";
        two.style.display="block";
        three.className="";
        four.className="selected";
    }
}