You would need to change it via deed poll which you can do online, however consent from both parents is required, otherwise you would need to go via court order https://www.gov.uk/change-name-deed-poll/change-a-childs-name
If he isn’t on birth certificate yes! Once baby’s dad is on birth certificate then he will have the same parental rights as you and it’s verrrryyy hard to change after that. Talking from experience
@Jodie so since he’s not I can do it no problems,
Yeah, just do it by deed poll, he has no parental rights to say anything if he’s not on the birth certificate x
And who do I contact to do this