You are unable to change your student username. Your username is a unique identifier for University of Otago systems as well as identifying you in information links between the University and the Ministry of Education (for example, your student index number) and WINZ.
Your username is generated at the time of your first enrolment and is retained in order to ensure continuity over the years with your changing status, including any changes of name.
Only in exceptional cases can a username be changed. Contact AskOtago if there are circumstances that might justify a change.
AskOtago SharePoint: Username creation resources