When an update to the Windows, macOS, or Ubuntu version is available and requires you to download the update manually, the game will notify you when it starts up. How you go about updating depends on how you bought the game.
Humble: This covers anyone who bought the game in a bundle, through the widget on our website, or through the Humble Store. If you added the game to your Humble Library, log in to your account and download the game again. If not, follow the link in the original confirmation email you got from Humble (it’ll look something like https://www.humblebundle.com/?key=xxxxxxxxxxxxxxxx). If you can’t find that link, get in touch using our Support Form, with as much information as you can (preferably the order email or Amazon or PayPal invoice number) and we’ll do our best to dig up your order details.
GOG.com: Either download the update from GOG.com, or download the update through the GOG Galaxy client.
Updates are automatically downloaded and installed if you bought the game on Steam, the Mac App Store, or Origin.
If you purchased the game through another storefront, download the new version from that same storefront.