Start the update, unlock your iOS device and go to Settings> General> Software Update .
There you can see the iOS 11.3 software update, a major 2.18 GB update. Make sure you're connected to a Wi-Fi network and grab a cup of coffee or something around the house, as it will take some time for the update to download. Once the download is complete, you will need to start the installation manually, which takes about 1
So … what's new?
Battery Health Tool (Beta Version)
iOS 11.3 brings a new battery health feature to indicate the long-term battery status of an iPhone and to inform users whether a battery needs to be replaced. These new settings can be found under Settings> Battery and are available for iPhone 6 and above.
This new tool comes in response to an Apple end-user review in late 2017 that quietly throttled iPhones and iPhones Many people with an older iPhone have experienced a surprisingly slow performance. After the investigation, Apple apologized for not publicly announcing why it does so, explaining that it artificially slowed iPhones with older batteries in iOS 10.2.1 to prevent an even more serious problem typical of older batteries is causing older iPhones to shut down unexpectedly. With this new battery status tool in iOS 11.3, users can now see how much capacity a battery has on a percentage basis and can replace it and avoid slower performance issues. A typical Li-ion battery is usually considered to be a replacement when it loses 20% of its capacity, usually after about 500 cycles, or about two years on average.
ARKit 1.5: Augmented Reality on Vertical Surfaces
With the launch of ARKit on millions of iPhones and iPads, Apple is leading the augmented reality in iOS 11, and now it gets even better: iOS 11.3 introduces ARKit 1.5, With AR-Apps you can now use horizontal surfaces such as tables and chairs, as well as vertical surfaces such as walls and doors. In addition, ARKit 1.5 now adapts better to irregular surfaces like a round table.
The view of the real world seen through the camera lens now has a 50% higher resolution and supports autofocus for a sharper perspective. 2D images such as signs, posters and artwork can now also be integrated into AR experiences.
New Animoji for iPhone X Users
Animoji was one of the coolest iPhone X tricks and iOS 11.3 introduces 4 new Animoji: Lion, Bear, Dragon and Talking Skull
The Business Chat launches as a beta in the US and is considered one of the largest stores in the nation including Apple, Discover, Hilton, the Main Depot, Lowe, Marriott, Newegg, TD Ameritrade, Wells Fargo and more. Many more partners should join in the future.
You can search for a business in Apple Maps, Safari, and Search, and you'll get a shortcut to start a conversation with it, just as you would start a conversation with a friend. Good news is that this is not a service that allows companies to spam them with their promos: only you can start the conversation and the company can not see any personal information about you unless you choose to ship or something else. Best of all, most conversations take place with a live agent, not a bot.
iOS 11.3 also adds a new Health Records feature that allows patients to view their medical records from over 40 healthcare systems, including Duke, NYU Langone, Stanford and Yale directly on their iPhone. The types of records that patients can see include lab results, medications, conditions, and more. Health Record data is encrypted and protected with a passcode, so it remains private and secure.
New Data and Privacy Settings
How does it work? If you use an Apple service that requires your personal information for the first time, you will be asked to allow sending certain personal information. A Privacy Icon Appears – Two Blue Silhouettes That Shake Hands – And Get a Detailed Explanation (19659007) This new privacy feature comes at the right time for Apple as more and more people worry about companies like Facebook and Google entering their personal information Advertisers or other sell parties. In contrast, Apple is building a privacy business as its core value. The company says this special feature has been in the works for months. Note that this new privacy feature is primarily a response to the EU's new General Data Protection Regulation, which requires companies to provide more transparent information about how to handle data. The GDPR Regularion comes into force on May 25th.
Other New Features
There are a number of other new features that you can find directly below: 
- Apple Music now streams music videos continuously through ads. Users can see the hottest new videos, classics, or those of their favorite artists in new music video playlists.
- Apple News makes it easier to stay up to date on key videos from The Day with a new video group in For You and improved top stories.
- Commuters in Beijing and Shanghai can use Apple Pay on their iPhone and Apple Watch for easy, fast and safe travel on metro and bus routes.  Apple TV App, a unified place for iPhone, iPad and Apple TV users to discover and launch the best shows and movies, is being launched in Brazil and Mexico. These markets join Apple TV app users in the US, Australia, Canada, France, Germany, Norway, Sweden and the UK.
- Brazil will receive Siri support for Apple TV 4K and Apple TV (4th Generation) Search and access movies, shows, songs, apps and more with just your voice.
- HomeKit software authentication offers developers a great new way to add HomeKit support to existing accessories while protecting privacy and security.
- Advanced Mobile Location (AML) support for automatically sending a user's current location when calling Emergency Services in countries that support AML.