You can change your plan at any time!
When you change your plan, you'll be charged for the new one immediately. You'll continue to get any boxes remaining in your old plan, then you'll automatically begin getting boxes for the new plan.
Existing subscribers - please make sure that you change your plan by clicking on the "change plan" text in your my account page. Please don't join again unless instructed to do so by customer support, as that might cause you to receive duplicate boxes.