Xr1st1naki The option would be in Steam since that's what you used to install the game. You can find instructions for switching between DX9 and 11 modes in Steam in this guide:
DirectX 11 (DX11) for The Sims 4 - A Step-by-Step Guide | EA Forums - 11811172
To answer the question in your other thread, about getting a black screen:
Try forcing the game to launch in windowed mode. Open Options.ini, in Documents > Electronic Arts > The Sims 4, and set fullscreen to 0 (zero). You can edit the resolution here too, but switching to windowed mode is more reliable.
If this doesn't help, remove Options.ini entirely and try again. This resets all your in-game options to their defaults, and the defaults should work fine.
It's fine to experiment with the in-game settings in general, even if you keep getting black screens when yo push things too far. At worst, you can always delete Options.ini again. And you can keep a backup copy of this file with most of the settings the way you like them, to have it on hand to restore when another change doesn't work out instead of starting from scratch with a new copy of the files.
Please keep to one thread from now on, at least until you've addressed your current issues.