delete apps from previous ID and set iPhone to factory seeting

I sold my iPhone to my friend and she used her apple ID to sync some apps and music but after few days she gave it back to me. now I have 2 questions : 1. how can I delete all her apps and apple id from my phone ? ( I mean I need to have it in original factory setting to use my own apps and apple id ) 2. I have a back up from my phone, how can I sync my own apps and use my own apple id ?

thanks guys