Find my biological parents?

How do l go about finding my biological parents. I am 26 and was adopted very young. Is there a dna test that l can take that will give me a direct answer? I don't have any relationship whatsoever with any of my biological family. My birth certificate was also changed when l was adopted. My fathers name was never on the certificate but maybe my mothers was. Should l try to obtain a copy of that? I am more interested in finding my father as my mother was abusive towards me as a baby. Tia.