Apple had released the beta version of OS X Yosemite 10.10.3 to public on March 2. Those of you who already registered as an Apple Beta Software Program can download and install it on your Mac. This pre-release version of OS X allows you to access the new update and new Photos app for OS X.
If you want to install this beta software but you have not already registered as an Apple Beta tester, first you need to sign up as a member of Apple Beta Software Program on this page.
Once you registered and signed in to that page, you need to download Yosemite Beta Access Utility (YosemiteBetaAccessUtility.dmg) and install it. Note that this is a BETA software. It is recommended not to install this software on your main Mac because it subjects to change and is unstable software. After you install the “YosemiteBetaAccessUtility.dmg” then check the updates on the App Store. The Pre-release of OS X Yosemite 10.10.3 public beta should be available. Click the Update button to install it.
Once you install the update, you have to restart the Mac to complete the installation. It may take a couple of minutes to finish the installation depending on your hardware specs. Verify the OS X version after it completed by clicking About This Mac menu.
Hopefully this brief article is helpful enough for you who want to install OS X 10.10.3 beta.