How to change baby's last name to his dad's last name in Wisconsin?

I gave my son my last name when he was born and now I want to change it to his dad's last name, because we got back together and now plan to marry. We have in Wisconsin until his first birthday to change it without going to court, but he turns one in just a couple weeks and I have to call a 1-800 number which I don't have and no one else seems to have. Does anyone know what it is or who to contact to get it?How to change baby%26039;s last name to his dad%26039;s last name in Wisconsin?
Call your local family court office which will be at your county seat (capital). You can also try to call your local office of vital statisitcs (where birth certificates are gotten from) and see what they suggest.How to change baby%26039;s last name to his dad%26039;s last name in Wisconsin?
Go up to your local courthouse to the records department and ask them there. Or you could call them. Look them up in the phone book.How to change baby%26039;s last name to his dad%26039;s last name in Wisconsin?
call your clerk of court, they should be able to help you, or the hospital may have info also on what you need to doHow to change baby%26039;s last name to his dad%26039;s last name in Wisconsin?
Only do it if you get married or want to keep his last name for ever