How to change add character library in Vocaloid4?

I've recently started using Vocaloid to practice making mustic as I can't sing myself, but I'm not sure how to make a new song with a different singer. I started out with Hatsune Miku, and I'm trying to make a song with Kagamine Len but I'm not sure how to import the Voicebank. Can anyone help?
Update: Sorry, I spelt music wrong