This is a Luma Patch for Animal Crossing: New Leaf that replaces some of the music with Animal Crossing related music from SilvaGunner. For a list of what was changed, please refer to the wiki page.
To install, simply make a folder called "titles" in /luma/ if it doesn't already exist.
Then, create a folder inside of /luma/titles named as the Title ID of the region of your game.
You can find the Title ID here.
Copy the contents of the downloaded .7z file to the folder you just made.
Next, enable "Luma Patching" in the Luma Settings, hold select at boot to go to the settings menu.
That's it!