Change Img src attribute using JS

img src js

HTML

<img class="fusion-logo-1x" src="//new.network-data-cabling.co.uk/wp-content/uploads/2016/08/ACCL_Logo.png" width="400">

JavaScript

window.onload = function() {
    document.getElementsByClassName("fusion-logo-1x").src = "//new.network-data-cabling.co.uk/wp-content/uploads/2016/08/ACCL_Logo.svg";
};