Here you can download the game client. There are multiple mirrors below so you can choose the best one for you. Once you are done downloading simply run the launcher and you'll be ready to play. Make sure you have registered a game account (website and game accounts are separate).
Dekaron Rising Installer 12.8 Download
(Updated December 16th 2016)
Option 1: Direct Download -- best to use a download manager with this one such as DownloadThemAll for Firefox
Option 2: Download from MEGA Mirror)