I want to change my kids last name. Their dad lives in Ohio I live in California, how do I this and can it be done without his consent?

can it be done without his consent?
Generally-no!

how do I this

Name changes require court orders.If you wish to change the name of your minor child, you will need to go through the court system to do so.
The factors that the court will consider in deciding whether to grant such a petition vary from state to state, but generally involve considering the impact such a change will have on the child and what the other parent's relationship with the child is like.