Since 7.6 has no official security updates, you must mitigate risks:
: The official successor, which maintains the core technology but follows a newer naming convention and licensing model.
: Reduces "boot storms" and improves performance for Citrix Virtual Apps and Desktops by caching frequently accessed data. Integrated Health Checks
If you're a Citrix customer with a valid license, you can also download XenServer 7.6 ISO from the Citrix Customer Portal:
How to Download XenServer 7.6 ISO (Full Guide)