Transferring macbook music to Imac music without deleting macbook history

My imac music is outdated compared to my macbook pro music (imac music has some of the songs on my new macbook). How do I delete the music entirely from my imac itunes library to transfer the new macbook music onto it?

P.S. I want to delete the imac music without it tampering my macbook music, despite them both having some of the same songs.