I cant upload any new music onto my iphone because im already connected to another iTunes library.

Basically, when I got my very first iPhone, I had connected it to an iTunes library on my laptop at the time.

Since then, that laptop has broke and I have my new one with iTunes on it. All of my iPhone's content is on this new iTunes apart from my music which it wont let me upload any other than what I have purchased on my phone. Every time I try to sync my music, it says that it will replace all of my iPhone's content for the content which is on my old iTunes. I do not want this to happen, is there anything I can do?