How can he change their last name to his?

my boyfriend has full custody of his 3 children and and wants to change their last name to his because she didn't want to put it into his last name when they were born. how dose he chage it now that he has full custody? will it cost anything? the children are all under 18 yrs of age.How can he change their last name to his?You can get the legal forms, instructions, and everything you need for him to legally change his children's last names at - http://www.legalformsbank.biz/namechange - for $19.95 and you can learn more about the procedure there.How can he change their last name to his?idk im not smartHow can he change their last name to his?He will need to go through the court system. This will involve filing a petition with the court for the name change, having a court hearing, publishing the petition for name change in a legal section of the newspaper for a certain period of time. There will be some expense, but every court has a different pay scale.