After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
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)
Download, unzip the file, drop into your assets/mod_overrides folder in the PAYDAY 2 directory. The track itself should be in "Options > Sound > Custom Heist Tracks"