Sub Main()
        Dim xml As String = "<root><cliente id=""001""><numero_cc>31010</numero_cc><valore>1000</valore></cliente><cliente id=""002""><numero_cc>31020</numero_cc><valore>1200</valore></cliente></root>"
        Dim r As New Random

        Dim x As New Xml.XmlDocument
        x.LoadXml(xml)

        For Each cliente As Xml.XmlNode In x.SelectNodes("/root/cliente")
            Dim valore As Xml.XmlElement = cliente.Item("valore")
            Console.WriteLine("Cliente: {0} Valore: {1}", cliente.Attributes.GetNamedItem("id").Value, valore.InnerText)
            valore.InnerText = r.Next
        Next

        Console.WriteLine(x.OuterXml)
        Console.ReadLine()
    End Sub