You will install the pak for UNITY-LIC-UPG-4.X.
The UCSS is a PAK as well, but you have to register it at www.cisco.com/go/license but you will be asked to input an ESW contract number which is your smartnet contract number for covering your software that you purchased. UCSS is a subscription per year that is required for major version upgrades.
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus