To update your registration details for an event on Eventzilla, first ensure that you are the order "buyer". You can log in with your registered email, select the event or order reference number, and click "Edit" on the order details page to modify your information. This could include your name, email, and answers to any custom event questions. Upon submitting the changes, a confirmation email with the updated ticket information will be sent to your registered email. For more detailed instructions, please refer to the Eventzilla Support guide.