You can change your Student ID by clicking on your name in the top right corner of the page, and then clicking on the "My Account" option. Navigate to the "Student IDs" tab, and you will see the option of changing your Student ID.

 

Some universities have multiple identifiers for different university portals. If this is the case, you can submit more than one Student ID for every course; you can enter one ID for Course A and a different ID for Course B, depending on what your instructor requires.