Changing last name if my son who has my last name to my husband's last name

First ANY question on law needs to include your general locale as laws vary by area.

I'm trying to figure out what your question is since it was so brief. But what I'm getting is that you have remarried and you want to give your son his step father's last name. If that is correct, you have go to court for a legal name change. This will also involve getting the bio father's permission for the change. An alternative is for the step father to adopt the child. But, again, that will require involving the bio father.

Is the child the bio child of the husband ? Or is there another father.

A name change will require permission of the father normally ( depends on where )
And/or good reasons for the change