While the rules of each state are different, the court where your previous orders are from can be modified after a petition to modify the orders in California has been filed together with a motion in the old state requesting that the court there relinquish jurisdiction to the State of California.

Because the rules are different in each state, you unfortunately usually need two attorneys: one to help with the filing in your old state, and one to file in California. Generally speaking, you can request this after you have lived in California for more than 6 months, but the longer the children have been out of the state of the previous order the more likely it is that the courts will agree that California is the proper state.

This is a hard process to do without an attorney, and the judges (one in each state) will use a set of factors to determine where the case should be heard, including where the witnesses who will testify live, the length of time the children have lived in each state, and where most of the evidence that will be presented can be produced.