I have developed a game for iOS that has had a decent amount of downloads, but I think I would get significantly more revenue if I were to convert the game to free to play, with in app purchases (especially since some competitors products are now free to download with in app purchases).
My question is what is the best way to go about converting to a free game with in app purchases without annoying the existing users?
On upgrading I'd like the people who previously paid for the app to have access to all the in-app purchases because I don't want to make them have to pay for content they previously had, and I don't want to make all the content (that is currently in the game) free.