If your GPU is from 2012 or earlier (e.g., GTX 600 series, HD 7000 series), SM 6.0 will not work—even after updating Windows. In that case, no software “download” can help. You need a hardware upgrade.
Microsoft introduced the "DirectX 12 Ultimate" branding to simplify this confusion. If your PC supports DirectX 12 Ultimate, it supports Shader Model 6.0. Shader Model 6.0 Download Windows 10
If you try to force-install an older DirectX redistributable, you will still end up with Shader Model 5.1. To get 6.0, you must update your operating system and GPU drivers. If your GPU is from 2012 or earlier (e