You can upgrade your account between packages at any point during your subscription, and you will be credited back for the unused portion of your subscription. You can also downgrade, but the downgrade does not allow for any cash refund, or credit to your account.
To upgrade please login to your account at http://forecast.predictwind.com/ on a Laptop/Desktop web browser (not a Android/iPhone/iPad).
Click on billing in the settings menu and choose buy now on the appropriate package.
Follow the steps to complete your purchase. When upgrading a refund will be credited to your next purchase for the unused portion of your subscription.