Yes, you can cancel your ticket at one condition: if you have purchased it from your account. You will need to log into it and following the procedure, at the end of the process you will receive a voucher for the ticket you have not used deducted the fee.
If you have bought the ticket out of your account you cannot retrieve the voucher and the ticket is not refundable. Yet you can amend it after the registration.
Any cancellation or amendment must be done before the date of departure.