Changing my daughters surname

[chels24]

hello i was just wondering if anyone could help me. my partner wants to put his name on my sons birth certificate. i dont have the farther of my sons name on the certificate as he wants nothing to do with my son. my partner has been there since day one and thats the only father my son has known so my partner wants to put his name on the birth certificate so i was just wondering if ayone knew how i would go about this as he wants it done A.S.A.P we have had a daughter together since then and she has his last name so we want to change my sons as well so he doesnt feel left out and we want to do it before hes old enough to realise it is different to his sisters so does that have to be at the same time or is it all different hope to hear from someone very soon thanks chels24 if you dont mind could you send your answer to my email add if you have time that is chelseabear54@hotmail.com if not just post it on here