Membership due dates cannot be changed. After a trial period has ended your regular membership payment will be charged according to the terms and agreements and every 30 days thereafter as long as one remains a member.
Regular membership payments are processed every 30 days based on when you signed up and when your trial ends. These cannot be changed, extended or altered in any way. As they are charged every 30 days, the day of the month may alter ie, they are not necessarily charged on the 1st of every month.
Your membership due date and amount can be viewed under your account > my membership.