To access the Beta branch on Steam, please follow these steps:
1) In your Steam Library Right click on Pillars of Eternity II, and select "Properties"
2) Select the "Beta" Tab, and click the Drop Down for labeled "NONE - Opt out of all beta programs", and instead select "Beta - Public Beta branch for upcoming patches"
3) Close the Window, and you should have a download ready. Attempting to play the game should automatically trigger the download.
How to switch back on Steam:
To switch back and opt out of all betas, simply repeat the Steps above, but select "None - Op