It's very EASY!

1. Download Unity Assets Bundle Extractor
2. Open UABE
3. Click on: File -> Open -> Locate folder named ,,BONEWORKS_Data" -> resources.assets.
(Sort by ,,Type", scroll to type ,,Textures 2D")
4. Find the texture you downloaded and select it.
5. Click on Plugins on the right side menu.
6. Select ,,Edit", down you see texture and on right Load.
7. Locate texture you downloaded.
8. Back in UABE - File -> Save.
9. Locate saved file and drag it to BONEWORKS_DATA and replace.
10. Done.
(In any case make backup files! You never know!)