This answer only really works if you don't need to do anything other than transferring the inner code (innerHTML) from one to the other:
// Define old parent
var oldParent = document.getElementById('old-parent');
// Define new parent
var newParent = document.getElementById('new-parent');
// Basically takes the inner code of the old, and places it into the new one
newParent.innerHTML = oldParent.innerHTML;
// Delete / Clear the innerHTML / code of the old Parent
oldParent.innerHTML = '';
Hope this helps!