Hi!
Step by step:
Install Il-2 Sturmovik: 1946 and you get version v4.07m.
The apply updates v4.08m, v4.09m, v4.10m, v4.11m, v4.11.1m, v4.12m, v4.12.1m, v4.12.2m one after another into the same folder, where you have installed Il-2 Sturmovik: 1946.
You then have the most recent version.
You have to have the same version like the server to join in Multiplayer.
Some of them require a mod pack.
You find all patches since Il-2 Sturmovik: 1946 here:
http://il2.jimdo.com/il-2-patches/