Let us pretend you ignore this guide and find a genuine DirectX 3.0a installer from 1996. Here is what will happen on a modern PC:
Locate the SA DirectX 3.0 package from reputable modding communities like Nexus Mods Extraction: Use a tool like to extract the downloaded files. Copy Files: Drag and drop all extracted files (typically including a and several folders) into your main GTA San Andreas installation directory. In-Game Configuration: Launch the game, go to Options > Display Setup > Advanced
Before starting, it is highly recommended to to prevent data loss if the mod causes instability.
Installing DirectX 3.0 would not upgrade your PC—it would downgrade it so severely that Windows would likely crash before GTA SA even loaded.
Follow this guide to get GTA San Andreas running without searching for the non-existent DirectX 3.0.