Cchild support modification?

Does anyone know about how much less my husband would have to pay his ex since we are adding my new baby to the case. Their taking 1376/ month he makes about 1500 a week before taxes but after tax n child support he brings home 700-900 a week. We have 2 boys our new born n i don't work so we are practicaly broke after payin for food saving for rent n bills i need an idea of how much it would go down. ..