How are the payment structures In the prosites payment scenario?

Hi,

It's my understanding that a Level Two subscriber will get the Level One + Level Two benefits.
Is that correct?

If I have two payment levels defined like this:

level 1 = $2
level 2 = $4

Does a Level Two Subscriber pay $4 or $6 per month?

If a subscriber upgrades to level 2 from level 1, what happens to the level 1 subscription?
Does he pay $4 or $6 per month?

Thanks,
Michael