If I have a child with a women who lives in Germany and I pay child support based off of what I made there but now make less money in the states, can I have my payments adjusted?

Yes.  Changed circumstances such as a change in income would be grounds for a modification of child support.

If your case was originally filed in CA, you would file an Order to Show Cause (court form) with the court requesting a modification of child support.  With your Order to Show Cause, you would file a supporting declaration stating the facts (reduced income) in support of your request for a modification of child support.  You should include pay stubs showing your current income.  When you file an Order to Show Cause, the court will schedule a hearing on the issue of your request for a modification of child support.  With these documents, file a proof of service.  You can either use a court form proof of service or you can write your own.  The proof of service verifies the date of mailing a copy of your documents to your ex (service by mail).  If you write your own proof of service, it just says that you are at least eighteen years of age 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 of the proof of service.  The date you sign should be the same as the date of mailing and the same date you file your documents with the court.