While classes start on 22 January, you have until 4 February to get your schedule set in stone. 4 February is what’s called the Add/Drop deadline, meaning that until that date, you can add courses or drop courses without consequence.
After that time, you may add or drop courses to your schedule, but it will come with a price and you will have to withdraw from the course.
Please look here for more information and the complete academic calendar.
If you have questions, let us know!