1. Open up Steam, and go to NEKO-NIN exHeart 2 Love +PLUS. Right click it, go to Properties, then Local Files.
2. Click on 'Browse Local Files'
3. Open the downloaded DLC in 7-zip. You should see this:
4. Click on the folder:
5. Copy the contents into the game folder. You should get this warning - confirm the replace files
8. Turn the game on and you should see this option, which indicates the DLC is installed