You can make the change online if the schedule change is reflected there. EWR and JFK are coterminals and the 3 hour change qualifies you for changes.
- Book the new flights for the day before, same day or day after, the original travel.
- Book identical routing if possible. It's okay to add or subtract a connection point or use co-terminals when necessary.
https://www.alaskaair.com/content/tr...-change-policy