EDIT: 1.2.8 Release out of beta, info here:http://forums.eagle.ru/showpost.php?p=2053590&postcount=1
If you are ok with overwriting your current install (please remember this is a BETA update) then you can update to 1.2.8 via Steam. Steps to do that:
1. Find DCS World in your Steam library
2. Right mouse click and access the 'Properties' menu (it's on the bottom of the list).
3. Click the 'Beta' tab on the dialog that comes up.
4. Select the beta 'open beta - Public beta versions'.
Steam will now update.
Note: It may be worth backing up your existing control/settings folder that lives here:
..as this beta via Steam will overwrite these. For beta bug reporting it might also be worth clearing the folder out so new settings are used, i.e. a clean slate. You can just rename your existing one (i.e. 127-DCS) and when 1.2.8 starts it will create a clean one. This will help bug reporting enormously.
1.2.8 Official Change Log here:http://forums.eagle.ru/showthread.php?p=2033920#post2033920