Hi Fritzl,
To get your IL2 1946 up to the latest version, the way OverDhill suggested will work.
As in: It will result in an IL2 1946 installation with which you can play online with the DD's. So, 4.12.2m, including the latest HSFX7.01
(It may lack in some skins, speech files or mission files. If you also want to do offline campaigns and do not want to miss any content, then you'll have to take a different route... I have tried it, starting with 1946 4.07m, then ran ChkMods, it works)
First, backup either the entire 1946 folder, or at least Conf.ini and the Users folder.
Then, follow the instructions in the thread OverDHill mentioned.
It will need to download a lot of files, in total some 7 to 8GB of data, how that will work out will depend on the speed and quality of your internet connection...
(As the amount of data is large, as well as the amount of files, it will probably not make it in one go. Simply restart ChkMods, and let it Verify and fix repeatedly... until it states no errors found)
Good Luck!