You cannot 'reset' something without losing data. The very definition of reset (in phone use) is to return something to a factory condition.
The nearest thing you can do is create a new user on the phone if it supports it. However if something happens to the phone while in your possession the data will be lost (there is a reason phones warn you to back up before updating, it can happen).
Why don't you just go out and get your own handset? That will be the easiest thing to do. It will be yours, factory fresh, new and complete with a warranty.