Simple id change won't work.

Simple id change won't work.

Hy
How do I change a id attribute of a div?
I would like to change the id of the nested div from a to b.
Here's my html

  1. <div id="image_wrap" >

       <div id="a"  style="width:500; height:375;"><ul><li>Funks</li></ul></div>

    </div>





And here's my javascript


  1. $("document").ready(function() {
  2.       $("#image_wrap div").attr("id","b");
  3. });
Please help.