Login to your Plesk control panel.
Go to the "Tools & Settings" option under "Server Management".
Choose the "Updates and Upgrades" option under the "Plesk" section. This will launch a new windows to choose components
Click on the ""Install or Upgrade Product" option at the top of the screen.
You'll see a list of "Available upgrade" options. Select the version 12.5 and click "Continue". (note, Onyx isn't supported yet, should be soon)
If there's any problems, the Plesk updater will display a warning before continuing.
If no problems are found, the upgrade will continue.
Click here to notify InfoQuest support once you've upgraded your Plesk version.
Support will synchronize your accounts Plesk version to your subscription.