Can you tell me how i could stop my dad from drinking beer?

Just talk to him: There is nothing magic about trying to help someone, although it may seem scary. Be open and honest, don't make judgements and don't nag. I advise people to tell their loved ones just that - they LOVE them, and want them around and healthy. Ultimately, people have to make their own choices. Have brochures from treatment programs available if and when he decides. Try Alanon meetings for yourself.