To install, run the installer and follow the instructions on screen.

...For Those New to Imperial Civil War...
New Era-Based Tech System
Play as the New Republic, Imperial Remnant or Empire of the Hand
Conquer Hostile Non-Playable Factions
8 New Galactic Conquests Scenarios
18 New Skirmish Maps
Redone Particle Effects and GUI
Dozens of new and Redone Units

...Major Changes From 1.0...
Fixed AI
Fixed Autoresolve
10 New Units
15 Completely Redone Units (Including 7 Empire of the Hand Space Units)
All Space Maps Redone With New Skydomes and Planet Textures
Removed Starbases Completely, Now Just Shipyards and Golans
See the ReadMe for a more complete list of changes
Delete all previous versions before installing 1.2