The best thing to do is see an experienced child support lawyer. They will run a new calculation for you, based on the change of marital status and differences in income.
Once you have the new calculation, you either get the other side to agree to it, or you take it to court and the judge will adjust it for you.
Q: How would I figure out what my ex-wife’s new spouse is earning?
As naive as it sounds, you ask him. You can’t force anyone to exchange information, but usually people will share it rather than go through the time and trouble of going to court. If worse comes to worst and there is still a lot of acrimony, then you may have to go to court to force that information from the new spouse.
The important thing is you want to do a calculation before you go to court and make sure it’s worth your while. If it will result in a small adjustment of support, it may not be worth the legal fees and court costs. Plus, it can backfire and you could find yourself facing a reduction in support.