As long as you have had the Daily Prepaid plan for at least 6 months you can keep your phone number and carry over any amount that is left on your prepaid account by calling customer service at 1-800-922-0204 and tell them you want to switch to the $50.00 plan. Believe this is a month to month plan.
Have you been using your prepaid phone for at least 6 months? Is your phone set up as a prepaid phone? I hope by now you have beable to get your $50.00 plan set up, if not call 1-888-294-6804