Except for the usual bug fixes and general improvements, there’s nothing new in this particular release compared to previous beta 6. This is likely the last beta release for iOS 9.3. At Apple’s media event next week, Apple is expected to release the final version of iOS 9.3 to public along with tvOS 9.2, watchOS 2.2 and OS X 10.11.4. Apple’s March 21st media event is also rumored to introduce new 4-inch iPhone SE, 9.7-inch iPad Pro and new bands for existing Apple Watch.
iOS 9.3 is a major release for iOS 9 featuring a new Night Shift mode, Touch ID/password protection to the stock Notes app, enhancements and improvements to other stock Apple apps such as News, Health, Activity and Music, 3D Touch Quick Actions menu for Settings.app and more, CarPlay enhancements, ability to connect multiple Apple Watch units to a single iPhone, Wi-Fi calling for Verizon iPhones, new enterprise features, and a lot more.
If you are already running any previous beta version of iOS 9.3, simply head to Settings > General > Software Update section on your iPhone or iPad to grab the latest beta 7 seed.
If this is the first time you are installing beta 7 of iOS 9.3, you will need to either get it from Apple Developer Program portal, or from Apple Public Beta Program site.