Updating config files dynamically

protected void EditConfigButton_Click(object sender, EventArgs e)
{
   Configuration objConfig = WebConfigurationManager.OpenWebConfiguration("~");
   AppSettingsSection objAppsettings = (AppSettingsSection)objConfig.GetSection("appSettings");    
   //Edit
    if (objAppsettings != null)

    {
        objAppsettings.Settings["test"].Value = "newvalueFromCode";
        objConfig.Save();
    }
}