Change image on hover

Question

How can I change this exact code to do the hovering effect on mouseover?

I tried following some of the other questions and answers, but I could not really follow the

Answer 1

Try the following code. It's working

I modified the code, like it will work with some delay in it.. But still, it is not animating..

function changeImage(img){
    // document.getElementById('bigImage').src=img;
    setTimeout(function() {document.getElementById('bigImage').src=img;},1250);
}