AFAIK, the only Norton subscriptions that allow monthly payments are the ones that include the LifeLock credit monitoring service.
The questions are:
- How do I make these Changes?
- What are the Implications if I proceed?
bjm_ already noted how you would have to achieve any changes you are asking about. There is no self serve option, and you would have to contact Norton Support to see if it can be done, and to ask them to arrange it for you.