Make sure to first have SuperBLT installed. Click the link in the dependency list.

Optional video tutorial for installing SuperBLT, BeardLib, and mod_overrides mods: 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. Drop that folder into the mods folder which is supposed to be in the game's installation folder (don't know where that is? click here)

Extract the ZIP
Place the folder inside the extracted zip into PAYDAY 2/mods/CustomOSTTracks
Boot up Payday 2
Select "Armstrong Style" in the music selector