All installs are set to the stable version of the game by default. To change this: 1. In your Steam client, go to the Library and right (mouse button) click on Arma 3
2. Select Properties (from context menu)
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3. Select the Betas tab
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4. 4.Choose either NONE for the Stable version or DEVelopment for the release candidate version of the game
5.Click Close in the lower-right corner of the window
Using the development version of the game could hamper your experience with the game, with some unfinished assets available. However, we would greatly appreciate your feedback. We intend this to involve you more directly in the development process and give you the opportunity to affect the final game. Your feedback and bug reports are welcome and can help us to improve the game significantly. Please visit http://feedback.arma3.com/ to learn how to submit feedback. Thank you kindly for your support! video tutorial from http://forums.bistudio.com/showthread.php?183552-Tutorial-Arma-3-RC-Branch-Install-and-Connecting-to-Testing-Servers