VMware NSX has four licensing editions: standard, advanced, enterprise, and remote office/branch offices (ROBO). Each licensing tier provides distinctive functionality, available per CPU socket on a perpetual basis at the vSphere cluster level.
The standard and advanced editions are also available as per 100 users in a pack basis to align with virtual desktop deployments (vSphere for desktop). The enterprise edition is also available on per-VM term basis. You can upgrade from standard to advanced/enterprise and from advanced to enterprise.
Prior to NSX 6.2.2, VMware NSX for vSphere did not have multiple licensing tiers. If you purchased NSX prior to May 3, 2016, you are entitled to VMware NSX Enterprise edition as long as you have active support and subscription contracts. You can upgrade your VMware NSX license key from the My VMware portal (http://my.vmware.com).