2nd hand computer and iTunes

I've been given a laptop from a friend who got a new one, its a mac and running the latest the software etc, but she's left all of her music on iTunes for me, yet when I plug in my iPhone, I can't put any of it on my phone and I can't seem to delete her stuff either! So, my question is, how do I make iTunes on this mac my own? Will uninstalling and then downloading it again fix the problem? I'm really not concerned with keeping her music. I've tried autherising the computer with itunes in my name, but that hasn't worked either…

I don't know much about iPhone, but try using a flash drive: create a folder on the flash drive, load the music then try using the folder to load the music to your phone.( the problem might be the incompatibility of software on iPhone and computer) if that fails then uninstall it and load your own music and you could always ask the friend who gave u the PC for help.