Most courts follow the federal child support guidlines when calculating child support payments. The guidlines are available on the net, college law library or from your attorney.
The only way I know to get your obligation reduced is to go back to court and have this done legally.
The reason I say this is, if for instance, you make an arrangement, in good faith, with your ex, outside of the court, to reduce support obligation. The court can and will come back in the future to collect what they will term as arrearages. Now, regardless of what you and your ex say will make no difference. They can and will collect the money or hold you in contempt of court and you either will pay or risk losing your freedom. Also, the court will probably not bother you until the termed arrearages reach a substantial amount, usually $5,000-$10,000.
So beware, be legal, once child support enforcement becomes involved they will collect.
Find and read the law president Clinton signed before leaving office regarding collection of child support. You should be able to find this on the net, law library or from your attorney.
Good Luck