how to change value of a node in xml document?

hi all,
This is my account.xml file:
<?xml version = '1.0'?>
<ACCOUNTS>
<USER>
<USERNAME>a</USERNAME>
<PASSWORD>a</PASSWORD>
</USER>
<USER>
<USERNAME>b</USERNAME>
<PASSWORD>b</PASSWORD>
</ACCOUNTS>

i want to change the value of node USER if i enter username & password in textbox = username & password in one node
for ex:
enter old username= "b"
enter old password= "b"

enter new user name ="c"
enter new password ="c"

-> change the value of node USER which contain user b
Result must be:

<?xml version = "1.0"?>
<MANAGE_ACCOUNTS>
<USER >
<USERNAME>a</USERNAME>
<PASSWORD>a</PASSWORD>
</USER>
<USER >
<USERNAME>c</USERNAME>
<PASSWORD>c</PASSWORD>
</USER >
</MANAGE_ACCOUNTS>

this is my script to do this:
<script language = "javascript">
<XML ID="customers" SRC = "accounts.xml"></XML>
function change_value()
{
var old_username = form.txtOldUsername.value;
var old_password = form.txtOldpassword.value;

var xmlDoc = new ActiveXObject("Microsoft.XMLDOM")
xmlDoc.async="false"
xmlDoc.load("accounts.xml")

customers.recordset.moveFirst();
while (!customers.recordset.EOF)
{
var currentUserName = new String(customers.recordset("USERNAME"))
var currentPassword = new String(customers.recordset("PASSWORD"))

if(username == currentUserName && password == currentPassword )
{

....//what code i have to write here to change

}
customers.recordset.moveNext();
}//end of while (!customers.recordset.EOF)
}
</script>

i don't know how to change the value of a node?
please help me.
Thanks..

This is really more of a javascript question. You need someone that knows the MSXML javascript syntax.

I can move this thread to the javascript forum if you like.

Thank you very much, but i can solve this problem by myselft.
Thanks...