After downloading the mod, use a program such as 7zip or WinRAR to extract the main folder of the mod.
Move the main folder of the mod to assets/mod_overrides. The assets folder is supposed to be in your game's installation folder (don't know where that is? click here for PAYDAY2 folder). Create the folder if necessary
To select the track, head over to your main menu and go to:
Options > Sound > Custom Menu Tracks
There you will be able to select the track in the desired menu by clicking on it and scrolling at the bottom of the list that pops up
