public  bool SetMachineName(string newName)
{
    RegistryKey key = Registry.LocalMachine;

    string activeComputerName = @"SYSTEM\CurrentControlSet\Control\ComputerName\ActiveComputerName";
    RegistryKey activeCmpName = key.CreateSubKey(activeComputerName);
    activeCmpName.SetValue("ComputerName", newName);
    activeCmpName.Close();
    string computerName = @"SYSTEM\CurrentControlSet\Control\ComputerName\ComputerName";
    RegistryKey cmpName = key.CreateSubKey(computerName);
    cmpName.SetValue("ComputerName", newName);
    cmpName.Close();
    string _hostName = @"SYSTEM\CurrentControlSet\services\Tcpip\Parameters";
    RegistryKey hostName = key.CreateSubKey(_hostName);
    hostName.SetValue("Hostname", newName);
    hostName.SetValue("NV Hostname", newName);
    hostName.Close();
    return true;
}

private void btnRename_Click(object sender, EventArgs e)
{
    var result = SetMachineName(txtName.Text.Trim());
    if (result) {
        MessageBox.Show("Changed Computer Successful.");
    }
}