First and foremost, you should obtain advice from a licensed California lawyer even if you plan to handle your own child custody case.The simplest way to request a modification of custody is to use California provided judicial council forms. Judicial Council Forms are the forms that the California court system has created to aid you in handling many legal situations. You can find judicial council forms on the California Judicial Council website. You will need to fill out at least two forms: [1] Order to Show Cause (Form FL-300) and [2] Application for Order and Supporting Declaration (Form FL-310). Start with these forms and add attachments as necessary. Once you have completed all the necessary child custody modification forms, you will need to file them at the courthouse where the original custody orders were made. Make sure to take the original documents and at least two copies. The court will keep the original and will stamp your copies. Some courts will require that you fill out County specific forms before you can file your documents. Depending on the court, you may also be required to obtain a mediation date before you can file your documents. Mediation dates can usually be obtained in another department at the same courthouse.After filing the documents, you will need to have a copy served on the other party or his/her attorney. Once all parties have been served, a proof of service should be filed with the court.