If you need to change your allocated stream, or have not been streamed into a class, you should contact the relevant teaching department.
It may be possible to request stream changes from academic departments, however there is no guarantee that you will be allowed to change streams. Some departments need to manage their streams very tightly due to resources and space in classes.
Timetable stream changes cannot be requested until the timetable has been finalised (usually the Friday before the start of the semester). Students are notified via email when the finalised timetable has been released.