A specific example:

- I do maybe a beta/alpha/pre-order for a game and set the full download for $10

- people buy that for $10

- after X months I raise price from $10 to $15 (as often some developers do) as the game gets near completion

Question: people who paid $10 will still get access to that item? or they need to pay the difference ($5)? or they need to pay again $15? It's not clear to me how this works :) thanks