Make sure to first have SuperBLT, and BeardLib installed. Click the links in the dependency list.

Ttutorial for installing SuperBLT and BeardLib: https://youtu.be/rin_sjSJIkg

1. After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
2. Navigate to PAYDAY 2/mods. (don't know where that is? click here).
3. Move the main folder of the mod from step 1 to the folder you navigated to in step 2.