Theres a few diffrent ways you can tell you parents.
The old "blurt it out" method seems to work if your parents arnt the type to go nuclear.
i used the letter method to tell my brother. just write a letter explaning the situation.
if your still in School, you could tell a teacher or a guidence counsler and see if they can help you tell your parents. also you can tell a sibling and have them help.
if ya wanta talk, feel free to pm me. Congratz and GL.