This contains two forms of syntax highlight, light and dark. To install you need to open notepad++, select the LANGUAGE tab in the top bar and select "Define your language". This will open up a windowy thing on the right. Select import and browse to where you extracted the themes and select the one you wish to install.
DARK THEME EXTRAS
If using dark theme make sure you go to the SETTINGS tab and select "Style Configurator". Under "Select Theme" pick "Twilight" and check the box next to "Enable global background colour".
Please let me know if there is any syntax highlighting I missed so I can update the file.