For Premium and Legacy Members, click the Cancel Premium button at the bottom of the My Membership page within My Account, which will opt you out of automatic renewal, allowing your Membership to expire at the end of the current term. 

If, after canceling, you want to opt back in to automatic renewal, only Premium Members may do so when manually renewing your Membership for one year toward the end of the term. During that transaction you may select to enroll in auto renewal, which will be applied to the following renewal, one year later.