If you are a current member of the All Access Pass Monthly Plan and are looking to change to the $14.99/mo Annual Plan, stop your current membership from your Account Info. Your subscription will be stopped at the end of your current billing period. At that time, you can select another plan from the Slate Digital website.
Also, if you're switching plans and have already downloaded the plugins onto your machine, you do not need to re-download the plugins. Just activate your license from the iLok License Manager and you're all set.