Here is my understanding of the update. As others I believe your primary source should be your OEM.
Main purpose: Ability to use SBAS procedures and navigation
The purpose of moving from UNS-1E to UNS-1Ew is getting the SBAS capability. From the UNS-1Ew manual:
The new “W” series of Universal Avionics Flight Management systems
incorporate the Global Navigation Satellite System (GNSS) Space Based
Augmentation System (SBAS) known in North America as the Wide Area
Augmentation System (WAAS). Other SBAS systems in the world will also
SBAS means using WAAS, EGNOS and other GNSS augmentation systems. SBAS in short provides for correction of GNSS radio signal propagation errors in a limited area. This increases pseudo-ranging accuracy and positioning precision.
SBAS (space-based) is opposed to GBAS (ground-based) where correction broadcasting stations are on the ground, like the DGPS, a surveying GBAS with a positioning precision up to 10 cm.
EGNOS measuring network (SBAS for Europe area):
Additional benefits of the update
From UASC documentation:
What else you get with an SBAS-FMS upgrade:
• Performance-Based Navigation (PBN) including Precision-Area
Navigation (P-RNAV) compliance and Required Navigation
Performance/Area Navigation (RNP/RNAV) up to 0.3 NM approach accuracy
• WAAS LPV / EGNOS APV, LNAV approaches
• Mode S Enhanced Surveillance support
• Accurate SBAS-GPS information provided to the onboard Terrain
Awareness and Warning System/Enhanced Ground Proximity Warning System
(TAWS/EGPWS) and Traffic Collision Avoidance System (TCAS)
• Large database capacity for worldwide navigation databases
You can read "The Benefits of SBAS" on UASC site.
And if you need more information the UNS-1Ew manual is also available.