Changing baby's Last Name

[aspau]

Hi sisses, please help I don't know how to change my baby's last name kasi nakasunod yun last name nya sa dad nya. I went to the city hall at sabi ng lawyer need daw ng dad's consent. My ex didn't want it to be changed kaya di daw sya magbibigay ng consent. I want it to be changed lang naman kasi para di na magkaaproblema pagdating ng araw kasi wala na ko plan hagilapin pa in the future yun ex ko.. please help....