Go to support.arubanetworks.com, login, navigate to Download Software, expand ArubaOS, expand General Availability, and then expand the next few folders, download the 6.3.x release that's applicable to your controller. Login to your controller, go to maintenance and image management, choose local file and browse to the image, choose the partition your not booted from and upgrade it. Once your ready to switch over you can reboot the controller under maintenance as well.