Please follow these steps to downgrade:

  1. Log in with your account and go to "Settings".
  2. Select "Subscriptions".
  3. Then click the grey "Show details" button.
  4. Click "Upgrade/Downgrade.
  5. Choose the plan you want and hit "Downgrade".

After the current month ends, your account will be downgraded and you will be charged for the "new" subscription.