You can get scaling and bleaching done from a dentist,,but this will help only the external stains to disappear,,if the stains are internal part of the tooth say something like fluorosis,,then you can go for intentional root canal treatments and crowns on front teeth.

Well, this could be due to fluorosis of teeth which occurs because of excess fluoride content in drinking water during the early years when permanent teeth are in their formative stages. You have to see a dentist and get an assessment done. Once the reason for the stains is determined, the next course of action can be planned. With the information currently provided, it is difficult to say anything more.