PRTG will already send an email to the entered email-address for the PRTG System Admin, once it detects an newer version of PRTG is available (this requires a direct connection to the Internet for the PRTG host).
As soon as a valid Admin-Email-Address is entered and emails for new todos are still enabled, PRTG will send out the notification about newer version. There is no explicit notification to add for this.
Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.