How do I get my charge brought to misdemeanor now that law has changed

I think you have to clue us in a little more. What charge and where. This is an international site.

I'm guessing that you were convicted of something which was a felony. Since the time of the conviction, a "Proposition 37", in whichever state it is in which you are located, was enacted, making the crime a misdemeanor instead. Do I have that right?

Unless the proposition specified that it would have retroactive effect, your conviction stands; you are out-of-luck, I'm afraid. Seek a pardon or commutation of sentence perhaps.

Almost no criminal law change is retroactive. So normally you do not get to change your prior conviction. If the crime happened before the new law was changed and you are arrested after the law was change, often you will still be tried according to the old law.

If it is possible will depend on the exact wording of the new law and in all cases would require a new court hearing, so you would need an attorney

I would certainly seek a consultation with a lawyer to see if the law that changed could possibly benefit me. What's to lose?