[6BL Bird-Dog]

To roll back firstly backup all the personal stuff in your programme ,ie stick controls,missions,skins etc ,(I always keep a backup on my system since one patch update deleted the lot). Log into Steam
Click on Steam in the upper menu
Select Settings
Under the Account tab, go to the Beta Participation section and select Change.
A drop down menu will appear. Select None-opt out of all beta programmes.
Select OK.
Steam will now restart and should update you files.If not right click the steam icon on your taskbar and select libary.Right click on the programme and select properties from the menue.
Open the local files tab .Verify the integrity of the game files,steam will check the files then download to the last alpha patch.Close the programme then re-launch to check for the correct version.
This is all at your own risk but has not let me down , at worse I re-enstaled the whole thing then placed my backups back in the relevant places.