Go to Sydney Student > My Studies tab > Units of Study > scroll down and click "AMEND YOUR UNIT OF STUDY SELECTIONS" > click "UNDO SELECTIONS"
To remove units, click the bin next to the unit on the list and then remove it.
To add units, click either Junior/Intermediate/Senior units box depending on which units you wanna add. Type in the unit of study you want to add under "Unit of study search". Your unit would pop up and you click "ADD" to add that unit.
If you're still stuck, there's a help guide link on the top of the page.
When you're done, click
SUBMIT > CONTINUE > CONFIRM > CONTINUE > EXIT once it tells you that it's completed