using System.Web.Mvc;
public class AdminController : Controller
{
    IMembersRepository membersRepository;

    public AdminController(IMembersRepository membersRepository)
    {
        this.membersRepository = membersRepository;
    }

    public ActionResult ChangeLoginName(string oldLogin, string newLogin)
    {
        Member member = membersRepository.FetchByLoginName(oldLogin);
        member.LoginName = newLogin;
        membersRepository.SubmitChanges();

        // … tutaj generacja widoku 
        return View();
    }
}
