Citrix XenApp and XenDesktop can be upgraded, but must be done in a particular order to avoid downtime. Prepare - run site checks, backup databases, check Subscription Advantage date, close apps and console and check permissions. Upgrade License server Upgrade StoreFront Upgrade Director Upgrade Provisioning Services servers and Target Device software Upgrade half the Delivery Controllers Upgrade Studio Upgrade XenApp/XenDesktop databases Upgrade remaining Delivery Controller