If you already own a license key, you can choose to upgrade to one of the larger plans in your account.
The cost of this upgrade is the current cost of the higher license minus the amount you paid originally. This does not include any renewals you’ve paid for.
For example, if you paid $39 for your license, and the professional license is $99, you would pay $60 for your upgrade.
Note: Upgrading your license key does not extend or renew it. You will retain your original expiration/renewal date. Upgrading and extending/renewing are two separate things with different costs associated with them.