Yes, if you are more than three days from departure. Change fees will apply. 

For changes being made three days (72 hours) or more from departure, and less than seven days from departure, changes incur a fee of $150 per passenger per direction not including taxes . For changes being made seven days (168 hours) or more from departure, changes incur a fee of $100 per passenger per direction. 

No changes are permitted less than three days (72 hours) prior to departure and change fees are non-refundable.  

If you have purchased ModiFly at the time of your booking it can be used to make change the date and/or time once at no cost for for all travellers. Details regarding ModiFly is available here.