Always back up your profiles and mod folders from Documents/Euro Truck Simulator 2 before switching versions. Downgrading can sometimes corrupt save files that were created on a newer game version.
After installation, launch the game. You'll start with a basic truck and a small amount of money. The game offers a tutorial that explains the basics of driving, loading, and delivering cargo. i euro truck simulator 2 version 145 download work
If you are specifically targeting version 1.45, these were the major additions that "worked" in that release: Hannover Rework Always back up your profiles and mod folders