XML database related problem

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C#

ASP.NET

XML

1.How to update the data to the XML database?
i have list of customer details.i have register page to get values.if click on the update button.the data has to update in the xml database.

<?xml version="1.0" encoding="utf-8" ?>
<!--Basic information of customer-->
<Customer>
 <Details >
  <RollNo>380567</RollNo>
  <UserName>Shruthi J</UserName>
  <DOB>19/10/1988</DOB>
  <DOJ>27/10/2010</DOJ>
  <Qualification>BE/BTech</Qualification>
</Details>
<Details >
  <RollNo>245615</RollNo>
  <UserName>Vishnuvardhan</UserName>
  <DOB>06/03/1986</DOB>
  <DOJ>18/04/2008</DOJ>
  <Qualification>Msc</Qualification>
</Details>
</Customer>

DOB and DOJ are Ajax Calender controls.and qualification is DropDownList. Please suggest how should i proceed to achieve this.

Thank you