My boyfriend has a child with a lady that lives in iowa we live in missouri. We never see him and have asked for a dna test.what can I do to lower the amount of support right now they are taking 50%

This is your boyfriend's problem and you have no legal standing.

HE needs to apply to Court, explain changed circumstances (or his reason for asking that the support be lowered), ask for a new Support Order. If he never sees the child he can ask for a visitation schedule, also.

50% is terribly high. 50% of gross or net?

Here's the support guideline: https://secureapp.dhs.state.ia.us/estimator/estimator.aspx

In MO, at least in the past, if he has a lot of past due support they may take 50 percent max out of a single persons pay. If he was married with a family there used to be a exemption and I think they can only take 25 or 30 percent.

Unless of course he did not provide them with income information and they are using a estimated amount that is no correct.