File a petition for modification of support with the appropriate court.
child support and visitation rights are two totally different things. The answer is no.
Apply to the court that issued the child support order.
I don't think they give child support for an adult. If your parents wants to support you great, but at 21 it is not a must.
no
... is possible on a showing that the obligor's income has changed substantially.
See related question below
Yes. It's a valid reason for asking for a reduction.
No, He has a moral obligation to support his child financially and emotionally. Unless his income has decreased support should remain the same.
No. Support and visitation are separate issues.
Unless the court order ordering him to pay child support specifically says otherwise, then yes. He could go to court to seek either to have visitation enforced or child support eliminated or reduced.
If the judge says so. Yes
Typically courts will not penalize a child by reducing support payments because a parent has had another child because this is not seen as being in the best interest of the child.