How to restore my iphone to the way i bought it?

I live outside of USA but my iphone was bought there and here there's no carrier that will work with cdma (no sim). I'm going to send it back but it has to be clean as if i'v never touched it altjough i have already acidentelly restored it with the data of my last iphone and now i don't know hpw to erase everything. I tried restoring it but it only erases somethings for example my apps but not my music. How do i restore it to scratch?

Plug it into iTunes and select 'Restore to Factory Settings'.

Go to Settings> General > Reset> Reset all Settings