You can use a program, or increase the "pre-amp" feature in the Equalizer, this sometimes distorts the music.
The best way, without adding a separate app or program (they often conflict with sound drivers and hardware), is to go to your playlist (if you do this click first song, scroll to the bottom, hold down shift and click last song, this highlights all the songs in the playlist), or an individual song.
-----> You can also do this in the main screen, highlight all of the songs.
Then right click on this highlighted area.
Click "get info", then click "edit items".
Click "options"
Adjust the volume, I increase it +80 or +100, then turn the volume down on the main screen.
this is for itunes ver 12.6.0.100 May 2017