Click on the person icon in the top right of your screen and select Account

Select the Subscription tab, in the subscription section you will see an option to Switch to Monthly or Annual.

Accept the confirmations and click on Switch.

Please note that for a switch from Monthly to Annual this will take effect and the end of your current monthly cycle. For a switch from Annual to Monthly this will take effect and the end of your current annual cycle. At any time before the switch you can cancel the switch by selecting Pending Cycle Switch button.

Accept the confirmation and select the Cancel switch button