you can set individual price tag for each downloadable file
So this is not actually true in the sense that I understand the sentence?
I know you can have tiered payment, like 0 for demo, 5 for game and 10 for extra.
But if you ahve 0 demo 5 game 10 extra 15 super extra, it is not possible to upgrade your payment tier. There is a thread somewhere asking for that feature, as it would make that possible. Another way would be to implement what the quoted sentence means (at least how i undrestand it)