Click on the Parallels Desktop menu, then click on Account & License to open a window with the list of licenses registered under your account.
If the license you would like to upgrade is registered under a different account, you can sign out from the current account and sign in to the one with the license. Click on the account email address in the activation window and select Sign Out. Then log in with the account you need.
In the activation window you will see the list of licenses available in the account. Click on Upgrade to Pro next to a subscription or a permanent license for Parallels Desktop to proceed with the upgrade.
You will get to your Parallels account page to proceed with payment. Here you will find the cost of the upgrade and the price of the subscription.
The upgrade cost is due at the moment of upgrade, it is the amount for the remaining period of your current subscription exclusive of the price you already paid for it.
The new price of the subscription is a full price for Parallels Desktop Pro Edition, with the exception of special offers. It will be charged on the billing date, when the current subscription period expires.