If you've already subscribed to an annual plan, you can switch your billing schedule to monthly at any point.
To change your billing schedule from annual to monthly, go to the "My plan" page from the main "Settings" menu:
Here you can review your current subscription plan, primary card details, and billing history information.
Click on the “Switch to monthly” link to change your current annual plan to monthly:
Then click “Confirm“ to complete the action:
You'll immediately be moved to the monthly billing plan!