Anyone paying or receiving child support can seek a review and modification at no charge through the Oregon Child Support Program. This link will explain how to request a review and modification and when you are eligible to get a review: http://www.oregonchildsupport.gov/services/pages/modification.aspx
You can request a review if it has been 35 months since the date the last order was entered or reviewed. You don't have to wait 35 months if you can show proof that there has been a significant change of circumstance since your order was finalized. Some examples of significant changes are:
If you want your child support reviewed or modified and it has not been 35 months and you are not sure if there has been a substantial change of circumstance, you can always contact an attorney. An attorney can help you file a modification proceeding. However this will involve paying attorney fees. If you can get an administrative review you won't incur attorney fees. So try contacting your local child support enforcement office first, to request a free review: http://www.oregonchildsupport.gov/offices/pages/index.aspx
WARNING: Once you request a review you should expect that this will launch a review and most likely a modification of your child support which may or may not give you a favorable result. So, you should always try to estimate if requesting a review will help you or hurt you before you initiate the process. The safest way to do this is consult with an attorney and have them help you with a preliminary child support calculation. You will need to have your income information and a pretty good idea of what the other parent's income is.
You can do a calculation online using this on line child support calculator to get an idea of what the new support amount will be: https://justice.oregon.gov/guidelines/. Be aware that there are administrative rules that allow rebuttals to the presumed support amount that you get from the online calculator. This means that you may be able to argue that the support should be more or less then the default amount. You will need the help of an attorney if you want to use any rebuttal arguments as this is a rather subjective area. You really need an expert to guide you. This page explains the allowable reasons for requesting a deviation from the presumptively correct child support amount: http://www.oregonchildsupport.gov/laws/rules/docs/050_0760.pdf