It’s not that often that Apple release a public version of their beta software for OS X, in fact they never have, well until today as they have decided to do just that with the release of a new initiative called the OS X Beta Seed Program, allowing users to grab earlier versions of OS X before they have even be released, and without having to pay up the £99 developer fee.
The first seed available is OS C 10.9.3, available to download now after you have installed Apple’s Beta Access Utility, which will make the new updates available on your system, however before you do, Apple does recommend that you backup your Mac first, which you can do by quickly setting up a Time Machine backup ahed of time.
After which you will also have to log into Apple’s beta website with your Apple ID, and accept a confidentiality agreement (stopping you from sharing any information about the pre-released software), after which you are ready to go.
We should however warn you, this beta software is not intended for use with the public (despite it being released to the public), and may cause various bugs and problems with your system, and as it does not provide any warranty coverage, or even support (there is a feedback form that you can use to report bugs, but no form to get bug fixes, those you will have to wait for), installing it is at your own risk.
If you do want to take that risk however, you can find out more at the link below.