All V-Ray Next users are eligible to upgrade to V-Ray 5. This will be an option until V-Ray 6 is officially released.
After V-Ray 6 is officially released the upgrade options will change.
You can find out your upgrade options by logging into my.chaos.com with your email address, locate your subscription under the Active Products tab and click on the Upgrade button. You will be presented with all the upgrade options available according to the version of your perpetual license.