how can I fix itunes to sync apps and musics?

I have used my own apple ID to sync music and apps for long times. About 5 months ago my friend installed a new app by his own apple ID on my phone and now unfortunately I can't sync any app or music. How can I fix this problem ? itunes version is: 12.0.1.26 IOS version is : 7.0.4 iphone 5s

thanks guys