WindowsPrincipal principal = new WindowsPrincipal(WindowsIdentity.GetCurrent());
bool administrativeMode = principal.IsInRole(WindowsBuiltInRole.Administrator);

if (!administrativeMode) {
    ProcessStartInfo startInfo = new ProcessStartInfo();
    startInfo.Verb = "runas";
    startInfo.FileName = Assembly.GetExecutingAssembly().CodeBase;
    try {
        Process.Start(startInfo);
        Application.Exit();
    }
    catch {
        //User denied access
        return;
    }
    return;
}