1. Backup your rendering.xml in 

(The Witcher 3 Wild Hunt\bin\config\r4game\user_config_matrix\pc)

2. Place the rendering.xml you just downloaded inside (The Witcher 3 Wild Hunt\bin\config\r4game\user_config_matrix\pc)

3. That's it.

The setting can be find under texture quality in your graphics options.

I prefer the setting on low or 0.2.

You may like having it at higher levels, experiment.

Happy Witchering.

Credit goes to Drogean for editing and putting together the original rendering xml