If my ex and I agreed to a specific amount for child support in our decree, can she change it after three years.

My ex-wife and I agreed to a specific dollar amount f child support in our divorce decree. I now learn that the state sends out a letter asking the parties if they want to modify the order every three years. The mount we agreed to was lower than the state may have calculated, my income has increased and my ex hate me so I fear she'll take me back to court for more money.