1) Go to LIBRARY, right click on Arma 2: Operation Arrowhead Beta (Obsolete) and select Delete Local Content... Click DELETE when popup appears. 2) Right click Arma 2: Operation Arrowhead and select Properties 3) Popup appears. Click BETAS-tab and select beta - from the dropdown menu. Click CLOSE. 4) The [beta]-tag should appear on your Arma 2: Operation Arrowhead once Steam has finished downloading. 5) Launch the game once manually through Steam! 6) Play DayZero through our Launcher! Don't have it? Get it here! After switching to the Steam beta branch, your GUID will be based on your Steam account rather than your CD Key, this means you have to whitelist yourself again! For information and guide, read this thread.