how to configure membership. So that at the end of the plan was to move to another plan?

I use the membership with a phased delivery of information.
I have the same flow of information but with different prices, depending on the term of your subscription.
Subscription for 1 month I have is $ 70
4 month subscription costs $ 150
and 6 month subscription costs $ 200
QUESTION:
How do I make it so
to a person in one month (or more)
when he paid only one month,
after the first month, could pay for the following four months (or 6),
getting access to sdeduet four months,
while remaining at the stage of presentation of information on which it is now. after the first month?
Thanks
with Respect
Yehoshua