ADViCE on surr name

eli

I have a son by a previous relationship my sons name is double barrelled by my surname and his, I now am pregnant with a new partner and his sur name is already double barrelled I do not like the first part of his sur name which is double barrelled which is his mums and last bit is his dads, can I drop out the first part of his sur name and replace it with mine.. so it would be my last name and his second part to his last name?