There is no change fee for Main and First Class fares on Alaska Airlines, but you may have to pay the difference in fare. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) Same-day confirmed changes and changes to Saver fares may incur a fee or have certain restrictions. 

Main and First Class fares

• There is no fee to change or cancel your flight.
• If your new flight costs more, you will need to pay the fare difference. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) If it is less, you will receive a refund for the difference.
• Exception for same-day changes: If you change your flight on the same day of travel, a fee may apply. Call at +1-888-415-1245 (US) or +44-203-869-5245 (UK) The same-day change fee is $50 for most flights, but is waived for elite members and those with refundable tickets.