If your husband is making the same amount as when the CS was ordered, you should be able to get it lowered. You will need to get the child support table for your state. Find the support amount for 1 child using yours and your husbands combined income. You then take that number and find out what percentage your husband contributes and what percentage you contribute to your combined monthly income.
The numbers are only hypothetical. Say your combined income is $10,000. You make 4,000 and your husband makes 6,000. That would mean that you contribute 40% and your hubby contributes 60%. Now say that the amount of CS for one child with parents that make a total of $10,000 is $1,000 a month. Your share of support is $400 and your husband share would be $600. He would then be able to deduct the $600 a month from his income that is used to calculate his child support due to his ex. If his paycheck is $6,000 a month, you would deduct $600 for the support of your child together. His income basis would then be $5,400.
It seems confusing, but it can be done.