How to tell parents I'm transgender?

Hi everyone, I am born a male but believe to truly be a female instead and have felt this way for over 4 years since high school and I am now 19 almost another year gone of not coming out to my parents after saying i would in new years. How did you come out to your parents? I have done everything to keep this a secret so they might think i am doing this for attention or messing with them when this is my reality that i am a transgendered woman stuck in a mans body. Please help me, i am tired of being trapped in this miserable body and nearly crying myself to sleep every day.