Make sure to first have SuperBLT, and CustomOST installed. Click the links 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. Navigate to mods\CustomOSTTracks. The mods folder is supposed to be in your game's installation folder (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.

You'll need Beardlib, SuperBLT, and CustomOst
After you install both of those open the mods folder and drop CustomOst in there
Drop the BL2RaidBoss folder in the CustomOstTracks folder

1. C:\Program Files (x86)\Steam\steamapps\common\PAYDAY 2\
2. C:\Program Files (x86)\Steam\steamapps\common\PAYDAY 2\mods
3. C:\Program Files (x86)\Steam\steamapps\common\PAYDAY 2\mods\CustomOSTTracks