How do I edit a specific node/child of an XML tree?

What is the best way to implement a way to edit a XML file with unknown nodes, subnodes?

For example:

    <root>
      <subroot>
       <name>
       <age>
       <adress>
        <street>
        <number>
       </adress>
     </subroot>
    </root>

Each node has a unique id, but every subroot could have more or less nodes than in my example (missing age, having 2 adress) like:

<adress> 
.....
</adress>
<adress>
....
</adress>

At the moment I am using the XElement class to write the id and following descendants into a file.

    if (element.Attribute("id") != null)
    {
        result = result.AppendLine(element.Attribute("id").Value);
        foreach (var item in element.Descendants())
        {
            result = result.AppendLine(item.Value);
        }
    }

I am using C# and want to be able to edit a specific <subroot>s content without knowing how many nodes it could contain. At the end, I have a form where you specify a subroot based on its ID and you are shown dynamically the appropriate amount of text boxes to change them.