I had serious reservations about transferring over, being a bit of a Luddite.
Couldn't have been easier.
Downloaded the image and created a USB stick.
Booted the device which was using OpenElec using the USB stick.
Selected the update option and let it do it's thing.
Re-booted the system, job done. It really is much better.
To be clear, any local media I am using is on the hard drive of the device so I can't comment on the process if it is stored externally. However all of my add-ons still worked, only better.