There are 3 important conditions that you should bear in mind:
Changing your topic only: If you wish to change your thesis topic and keep the same supervisor, then you need to do the following:
Changing your supervisor: If you wish to change your supervisor, then you need to do the following:
In both cases, the CSE Thesis Coordinator will need to approve the change and you will be informed in due course whether the change is approved.
If you have already enrolled in Thesis Part A and have a SY or withheld mark you will need to seek advice from your new supervisor and the CSE Student Office. You may be required to re-enrol in the course if your new topic is significantly different from the old one.