Try this:
DateTime dt = (DateTime.UtcNow.Day, DateTime.UtcNow.Month, DateTime.UtcNow.Year, DateTime.UtcNow.Hour, DateTime.UtcNow.Minute, DateTime.UtcNow.Second);
lblUpdate.Text = dt.ToString("dd/MM/yyyy hh:mm:ss tt").Replace('-', '/');
OR
lblUpdate.Text = dt.ToString("dd/MM/yyyy hh:mm:ss tt");
Hope it helps!
--Amit