Yes, you can. However, you have to do so as soon as possible, i.e. within 7 days after you have enrolled.
However, within these 7 days, you have to ensure that you have not already viewed more than 50% of the study material online and you also need to write a letter indicating why you wish to cancel the course. Telephone and email cancellations are not accepted. Make sure you read the terms and conditions properly.