How to sync my iphone with my macbook air without deleting all my old music?

I had a toshiba which had all of my music on and i had that music on my iPhone but know i have a mac and I want to put a new album onto my phone but whenever I try to my mac air says that I will delete all my other music. I have tried clicking manually managing my music but then when i click apply it says it will delete all my other music.

You ram your phone into the screen of the "macbook" and it should smash the your done! NOT really you need ITunes

You can backup the music on iCloud, then sync itunes.