It's easy to change your membership plan from Game Saver to All Access (or vice versa).
You will simply need to cancel your current subscription and initiate your subscription to the new plan which may easily be done via your account pages. Note that your monthly recurring billing date will change to the date your new subscription plan is initiated.
Example: Today is September 10. If you are a current Game Saver member whose re-billing has traditionally taken place on the 5th of each month and you switch plans today, you will be billed today and your new re-billing date will be on the 10th of each month going forward.