Sort them~

sortem

var downloadables = document.getElementsByClassName('download-links');

for (var op = 0;op < downloadables.length;++op) {
    var list = downloadables[op];
    var items = list.childNodes
    console.log(items);
    var itemsArr = [];
    
    for (var i in items) {
        if (items[i].nodeType == 1) {
            itemsArr.push(items[i]);
        }
    }
    
    itemsArr.sort(function(a, b) {
        console.log(Number(a.firstChild.innerHTML));
        console.log (a.firstChild.innerHTML - b.firstChild.innerHTML);
        return $(a).data('res') - $(b).data('res');
    });
    
    for (i = 0; i < itemsArr.length; ++i) {
        list.appendChild(itemsArr[i]);
    }
}
    
  <ul class="download-links">
      <li data-res=540><a>"540"</a></li>
      <li data-res=360><a>"360"</a></li>
      <li data-res=720><a>"720"</a></li>
      <li data-res=1080><a>"1080"</a></li>
      <li data-res=480><a>"480"</a></li>
  </ul>