How do I officially end it all with my parents?

I am an adult in my thirties, and I will never have anything to do with my parents, who are in their 60's. No contact, no funerals, nothing. Can I "disown" my parents? I don't believe in leaving things hanging or unclear so just ignoring them from now, or paying for their decisions for that matter, on is out of the question. Is there a customary or even legal way to do this, like a letter of notification sent to them? I do plan on writting a letter but am unsure of the proper way to write it, legally as well if there is a difference.

I have other family and am not breaking off any other family ties - just with my parents. So, I wouldn't be disowning myself from my family, just my parents from myself, or myself from my parents.

Any tips?