If the classes you wish to choose clash, you will need to select an alternative class. Go to My Class Registrations and swap into a different class.
Prior to classes starting, new places become available in full classes from time to time. If you're keen on a certain class time, check My Class Registrations regularly to see if a new place has opened up.
If your class timetable shows you have successfully registered with a clash, check your timetable week by week. It is likely that you have classes that alternate either on a weekly, fortnightly or ad hoc basis that may appear, at first glance, as a clash. To view your timetable for a particular week, click on the My Calendar tile and select a date range.
Still have a clash? You will need to change one of the units you're enrolled in. Check your course planner to choose another unit and then check My Class Registrations to see if the timetable will suit.