To change your name, you need to visit the Student Centre. They will need to see suitable evidence of your name change (passport, marriage cert, deed poll, etc.) and your student ID number. In most cases, the team will update your record, scan the document, and issue you a new Greenwich Gateway (Student ID) card.
In the rare occasion the team are unable to update your record, this will be explained, but this is usually because you have officially completed your studies.