Manipulate XML

I want to convert from XML1 to XML2. Is it possible to do this through set value? Or, do I have to write a custom script? I want to group the repeating elements by the id and merge it with the form as buckets of data...

XML1

<form1>

     <Details>

          <id>1</id>

          <firsntname>example1</firstname>

          <lastname>example1</lastname>

     </Details>

          <Details>

          <id>2</id>

          <firsntname>example2</firstname>

          <lastname>example2</lastname>

     </Details>

     <Details>

          <id>1</id>

          <firsntname>example3</firstname>

          <lastname>example3</lastname>

     </Details>

     <Details>

          <id>3</id>

          <firsntname>example4</firstname>

          <lastname>example4</lastname>

     </Details>

</form1>

XML2

<form1>

     <Details>

          <id>1</id>

          <firsntname>example1</firstname>

          <lastname>example1</lastname>

      </Details>

     <Details>

          <id>1</id>

          <firsntname>example3</firstname>

          <lastname>example3</lastname>

     </Details>

</form1>

Aditya