Sync iPhone without losing music

I recently bought a new macbook and i was wondering if there's a way to sync new songs i download(without paying for) to my phone and not lose all the music i have on it now?

Itunes will erase all the songs you previously had and will add mew song…

You can try copy trans manager, its very easy, you just simply need to connect your iphone and open up copy trans and select your songs and drag all to the your iphone's song list in copy trans and click on update on top and you can add new songs without deleting old songs