Refresh FCK edit area when change value under external scrip

Hi All!

I have a problem with refreshing FCKeditor edit area when I put some new value under external script...
Here is some part of code:

Creating editor under PHP5

$oFCKeditor = new FCKeditor('htmlmessage') ;
$text = "some here to edit";
$HTMLmessage = $oFCKeditor->CreateHTML() ;

And here is button code:

<script language="javascript">

function update()
{
   var msg = document.getElementById("htmlmessage"); 
   
   alert (msg.value);   
   msg.value = "new";
   alert (msg.value);
}
</script>

On second alert i see new value.. but on editor shows old.. how to refresh editor?
Thanks.