My open alpha install is 71 gb....7.8gb which are extra files mainly skins.
As per Bignewy:
Anyone who has not tried a cleanup and repair here is a short guide
Remove your user mods if you have any, and backup any changes
go into your Eagle Dynamics/DCS World Openalpha/bin folder.
There, hold Left Shift and right click and click "Open Command window here."
Then, type the following exactly as printed:
DCS_updater.exe cleanup
this will delete all non official files
then do a dcs repair
DCS_updater.exe repair