1. If you want to change the topic that has been submitted to the system at the beginning of the paper, you can communicate with your tutor and see if you can change it. If you can, how to operate and how to follow the process will be subject to the requirements of the school.
2. If it is a final paper uploading system, and even after the defense, you need to change the topic, just change one or two words. You can communicate with the tutor to see if the opinions of the judges and teachers are worth adopting.