You need to have a valid support contract on the ZD in order to upgrade it to any version.
If you already have a support contract, please download the entitlement file from the below link and upload it on the controller under Administrator> Support and try the upgrade.
https://support.ruckuswireless.com/entitlement_fileIf you don't have a support contract, then reach out to your partner or local sales and buy one for the controller.
- Anusha