Make sure you have full control on your Dekaron folder (properties>Security>edit permissions)
Then navigate to Dekaron>History or Launcher.config and change 1.2.8 to 1.2.9. Save it, exit and launch again. (I forget which config folder it is, think it's the history one)
If it is not updating check what version of the client it is sticking at and follow the above instructions using the 'stuck' version number. If that doesn't work try restarting your PC before trying again to make sure nothing is running in the background which may be preventing the client from completing
"Navigate to Dekaron folder > Open as notepad file "History.config" change 1.2.8 to 1.2.9 also if you find a diferent number like 1.3.0 just put the one foward like 1.3.1) Save it (probaly if he doesnt allow you to save in place save it on your desktop them copy back to the folder), exit and launch again."
Comments
http://dekaronrising.com/index.php?/topic/20936-guide-fix-game-and-launcher-issues/