Only teachers have the ability to archive old Subjects.
Archived Subjects are removed from your home page to reduce clutter.
Subjects that have remained completely inactive for a few months will be automatically archived by Stile, however if anyone clicks around in it (including you!) then that inactivity will reset. You can ask your teacher from that Subject to archive it or remove you if you no longer use it.
You may also be interested in the following resources: