How can I transfer iTunes content from 1 mac to another

I have 2 computers,1 is an iMac and the other is macbook pro,i have 2 iPhones 1 synced to each computer,I need to change the content from 1 mac to the other,cause me and my girlfriend have iPhones and we are breaking up and I'm giving her the macbook pro,but her phone is synced with my iMac..How can I do all this so we can have our phones in our computers once she leave..i have phoneview but i don't know if that is what I need,or is there anyway we can delete our iTunes content and sync our iPhone like if it was a new..any help will be appreciate it

This only works to transfer music