window.onscroll = function (e){
    var wMenubar = document.getElementById("wMenuBar"),
        wLogo = document.getElementById("wLogo");
    if(window.scrollY > 50){
        wMenubar.className="small";
        wLogo.src = "logo-small.png";
    }else{
        wMenubar.className="big";
        wLogo.src = "logo.png";
    }
}