As a Mac App Store customer of Moom 3, you are entitled to a discounted upgrade price for Moom 4.

We've tried to make that process as simple as possible: You can upgrade from within Moom 4 itself, and we'll attempt to migrate your App Store purchase to a direct purchase.

But if you have any troubles with that, or you'd like to better understand your options, please read our in-depth crossgrading page.