You can go to your subscriptions on the FITE app or the FITE website and then click on your AEW subscription - you will find the option to upgrade there.
For subscriptions started on Amazon and ROKU you will be able to start a new yearly AEW Plus subscription after your current monthly subscription ends. You will need to cancel its renewal first by following the steps in this article. Once the pre-paid month ends you will see the option to start a yearly subscription. The AEW Yearly option will be open until MARCH 31st.