First, log into your profile. – Then use the drop-down arrow on the upper right. Click on your name once it has dropped down.
In the middle of the page you will find your current information on your Subscription Tier
You may also upgrade your subscription. The upgrade will charge you the difference between the two subscription packages, and you will then check out. Credits will be added immediately.
If you choose to downgrade the downgrade will take effect at renewal.
Last, canceling the subscription will cancel affect the date of the next renewal.