You can do this by logging into your online My48 account.
See here:
What is auto-renew?
Auto-renew allows you to set up a monthly recurring payment to renew your membership automatically so you never forget. As we're a prepay service you'll need to purchase your membership monthly to continue to receive the allowance you want. With auto-renew it takes the manual effort out of buying a membership so you're never without your allowance. Auto-renew is on by default for all new customers after you buy your first membership. You can turn this off in My Profile under Payment Details. Just a heads up - payment details can only be added/edited through the web version of your My48 account.
