var configuration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~");
var section = (System.Configuration.ConnectionStringsSection)configuration.GetSection("connectionStrings");
section.ConnectionStrings["MySqlConnection"].ConnectionString = "Data Source=" +
txtserver.Text + ";Initial Catalog=" + txtdatabase.Text + ";User ID=" + txtuid.Text +
";Password=" + txtpwd.Text;
configuration.Save();