I got a new iPhone and its not letting me back up?

My iPhone 16gb 4s got stolen so my friend gave me her iPhone 4 8gb phone i tried to back it up but it won't let me its says there not enough memory and the option of choosing like unpicking music etc is not coming up is, is there anyway i can go and delete things from the back up to make enough room i have no iCloud back up

Plug it into iTunes, and back it up from there.