Select it, and Steam will automatically begin downloading the 1.38 files. Official Free Trial
The latest update, version 1.38, brings several new features and improvements to the game. Some of the key changes include: Euro Truck Simulator 2 1.38 Free Download
Verdict: There is no legitimate “full game free download” for ETS2 1.38 unless you already own the base game. Select it, and Steam will automatically begin downloading