Daily builds of Ubuntu 13.04 – Raring Ringtail – are now available at http://cdimage.ubuntu.com/daily-live/current/. This will be the only way to get Raring at present, because the alpha releases have been dropped.
Right now, there is no reason for most of us to upgrade. There are not many changes from Quantal as yet. However, the release of daily builds means that the new development cycle has officially kicked into gear.