Subscription Level Meaning

I currently have 4 subscriptions. Two of which are level 1, and two are level 2.
The level 1 are similar in access, but are package A Monthly vs package C Yearly, While the Level 2 are premium package B Month vs package D Yearly.

How does this effect Upgrade and or downgrade?

Basically I want upgrade to be immediate, and downgrade, at the end of the cycle.

For instance, each package increases in A, to B to C to D. If someone moves from A to B or from B to C he pays the difference, and upgrades, alternatively if he moves from D to C or C to B he will wait until the end of the cycle and move.

How can that be changed? Is the change immediate?

Subscription Level Meaning
 
 
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