Can I contest an already finalized divorce

I was divorced nearly 4 years ago in Texas and since have moved to Wa. St. and my Ex to San Diego Ca. I have since been forced to take a massive paycut of about $15,000 a year (huge from a lower middle class perspective) from what I made then yet still am forced to pay a large Child Support sum. My Ex however has lost her 5th job in 10 years and 3rd in 5 years. Is there anyway that I can fight/contest for custody of my child and relinquish my ex's rights to receive child support due to her inability to provide a stable home for our daughter? - Is this your question? Add additional information