Patch difference from 0.4u is 754.8MB
If you backed through the Humble Store, you can simply download the newest version via your widget purchase reward content.
If you are a Kickstarter backer with a Steam beta-unlock key, please make sure you opt into the correct beta for your platform. Please note that the first release (and current patch) is windows only. We'll release the Linux/OSX versions once we've fixed the compute shader bug.
You can do this by right clicking Koe (声) in your Steam library, selecting "Properties", clicking on the Betas tab and opting into one of three beta builds, select the correct one for your operating system. The default beta ("beta - ") is Windows.
The Kickstarter update related to this alpha release is available here:
https://www.kickstarter.com/projects/297265509/koe-a-jrpg-with-japanese-at-the-core-of-gameplay/posts/2467725