While the answer to this question seems like an easy yes, the real answer is maybe. Let me explain why.
Suppose you were divorced 10 years ago, have two children and were earning for child support calculation purposes $60,000. The formula child support would be 25% and so you would pay $15,000/year or $1,250/mos for two children. Fast forward to the present and you are earning $100,000 for child support purposes and are still paying $1,500/mos and your oldest child just turned 21. The immediate thought is to reduce your child support since you only have to support one child. However, the court will recalculate your child support amount based upon your current income. So your newly calculated obligation would be 17% which would be $17,000/year or $1,416/mos.
So if you were to file to for a downward modification to recalculate your child support obligation, you would wind up with an order directing you to pay more. So my advice would be to do nothing and keep it at the existing amount as long as you can and save the money.
Keep in mind that the amount of change in support is not evenly split between the number of children that you have. The child support percentages are 17% for one child, 25% for two children, 29% for three children, 31% for four children. So what happens is that there is not a big change going from four to three or three to two children. So my advice is do the math before you file for an adjustment.