I currently pay support on both children in TN and I live in FL, my son has just moved down with me so my daughter is still with her mother. What form do I need to file so support is dissmissed being we both now have one child each.

So someone went back to court and got the child custody agreement changed, so that one parent has legal custody of one and one parent has legal custody of the other ?

The support should have been changed then.

You can not just ship one child and think support is changed.

You will have to file and go back to court to change custody, to change child visit orders to give both parents visits with the other.

And the parent with the higher income is still most likely going to be paying some support, just not as much.

Child support is ordered by a court. It can only be changed by a court. If one child moved in with you and you didn't file for a modification of the custody order, then as far as the court is concerned support doesn't change.

You need to go back to the TN court and file a petition for modification of both the custody and support orders.