Default Back to stock? Rooted Virgin Mobile Galaxy S3

I have a rooted Samsung Galaxy S3. It's got the carbon rom and 4.4.2 android software. Basically, I would like to return this phone to the stock specs so that I can sell it and upgrade to an S5. Is there a way to return to stock to the point that another user can set up a Virgin Mobile account on the phone? I've been trying to research the subject throughout the forum but I haven't found a solution. Any help would be greatly appreciated. Thank you.