My mother was adopted and she ped away 15 years ago. How do I find her birth parents?

I'm trying to find out how to find her real parents. Not to meet them but to just get some information. I would like to know my heritage and my families medical history. My mother was also an alcoholic and I would like to know if it was hereditary cause if so then I need to know so I do not become one in the future. I don't have the money to pay lawyers so I was wanting to know all the differant ways there are for going about it. Thanks.