You can change your auto-renewing subscription to a non-renewing one by selecting "Cancel - At end of term" on your Customer Portal page. 

Selecting the above option will cancel your subscription once your current term is completed (e.g. if you selected a 3-Month Plan, you will receive your supplement pack for 3 months, and thereafter your subscription will get cancelled and will not be renewed).

If you want to resume your subscription later, you can select "Reactivate" on your Customer Portal. A new invoice will be generated, and on successful payment, your subscription will get reactivated.

If you just wish to take a short break, "Pause subscription" might be a better option. Lets say, you are on a 3-Month Plan, and after receiving your third month's supplement pack you want your subscription NOT to auto-renew at the end of the third month. You can pause your subscription for upto 90 days on your Customer Portal. 

Do note that "Pause" suspends your subscription for the selected period (you will not receive any shipments during that period) and is not the same as "Cancel at end of term".