How can I get the maintenance payments thatI make to my ex-spouse modified?

Changed circumstances such as a change in income is one of the legal arguments which will support a modification of spousal support. 

From the court clerk, obtain an Order to Show Cause (court form).  Complete the form requesting a modification of spousal support.  File  with the court the Order to Show Cause with your supporting declaration of the facts stating your reasons for the modification of spousal support signed under penalty of perjury and an attached proof of service.  When you file the Order to Show Cause with the court, the court will schedule a hearing on this issue.  The proof of service verifies the date of mailing to your ex.  You can use a court form proof of service or you can write your own.  If you write your own proof of service, it just says that you are over eighteen and the attached documents were sent via first class mail unless stated otherwise to _________ (name and address of your ex) on _________ (date).  You sign and date at the bottom.  The date you sign the proof of service should be the same as the date of mailing and the same date you file your documents with the court. 

Check with the court clerk before filing to be certain you have included all the necessary documents for requesting a modification of spousal support as the required documents may vary from state to state.