modify Xml page

Question

Hi,
My Xml page looks like this as follows:

<?xml version="1.0" encoding="utf-8"?>
<phone>
  <person id="1" name="tet">
    <phoneno>675765876567</phoneno>
    <city>st</city>
  </person>
</phone>

In this i want to add another value in the name attribute as

<person id="1" name="test,sample,testing,......etc">

how to perform this using C#.net.please help me
Thanks in advance