Reopening a Divorce to Disestablish Paternity

[Piscis]

My question involves paternity law for the State of: NYC
I need to reopen my divroce to destablish the paternity of my ex husband, and establish the paternity of my son's biological father. I broke up my my first boyfriend when we already had a child, and not knowing that I was pregnant. being young and stupid, I quickly married a friend who understood the cultural and family pressure I was undergoing not to have a second child out of wedlock. It did not work out, and we got divorced, amicably, and even though the divorce stated that he was the father and that he was to pay me child support, I never sought it, because we both knew it wasn't his child. I am now back together with my sons' real father and have been together since the divorce. We want to change my youngest son's last name to match his real father's and his brother's, but we my ex and I were told that we need to reopen the divroce for this. I want to know how hard is this going to be if we are all accordance and want to change the name. How long will it take? My youngest has known his real father as his father and thinks of my ex husband as his "uncle", since we divorce when he was about 4. He hates to have a different last name than his brother. Please respond soon, this is really stressing me.
Thank you.

[Mr. Knowitall]

If your ex-husband is in agreement, I don't think it will be particularly difficult for a lawyer to reopen your divorce and disestablish paternity. I do think it's likely to be tricky to do yourself, but if you can figure out the legal processes for doing so you can proceed without a lawyer.