If you are able to tell them you have to do so that you live in peace with them and with yourself. This is the only logical solution. You will have to face them with your decision one day and now is as good as any.
But if you are afraid for your life that they may hurt you or kill you (which is not normal), you may postpone telling them and you may skip this party by claiming to be ill or tired.

I’m 16 years old, and I embraced Islam without my parents knowing. Today is my birthday and they want to organize a party for me. People will come in my home,our relatives,What to tell them? Because they will put music, and is haram to celebrate birthdays