You can cancel whenever you want. You are auto-billed monthly on the day that you first sign up to Premium, each month. You can cancel at any time. However, if you cancel, you have only 30 days to move your site to another host (if you buy your own domain) before they delete your site. Also, you cannot return back to the free version and keep all of your work. You will need to start over from scratch. Keep in mind, you will still be in the system as a free member just in case you decide to upgrade again in the future.