Users iPhone, iPad, and iPod can install the update by clicking 'Check for Update' in iTunes devices. Similarly the Apple TV 2 users can also download the 'Check for Update' is available on the device.
Link IPSW updates provided MacStories also can be downloaded on the iPhone 4, iPhone 3G, iPod touch third and fourth generation, iPad, and Apple TV.
About Apple iOS 4.3 Software Update, new features and improvements, including the following:
1. Personal Hotspot
Share iPhone 4 cellular data connection with up to 5 devices (combination of up to 3 Wi-Fi, 3 Bluetooth, and 1 USB)
2. iTunes Home Sharing
Play music, movies and TV shows from a shared iTunes library on a Mac or PC (requires iTunes 10.2)
3. New AirPlay features
Play videos from the Photos app including the Camera Roll album, iTunes previews, enabled third-party apps and websites on Apple TV
Play slideshows from Photos on Apple TV using transitions available on Apple TV
4. Faster Safari performance with Apple Nitro JavaScript engine
5. HD video out using the Apple Digital AV Adapter
View 720p HD videos from Videos app, iPod app, Photos, YouTube, Safari, Keynote, and enabled third-party apps on an HDMI display
6. Ping features
Push notifications for comments and follow requests
Post and Like songs directly from the Now Playing screen
Parental controls
7. New Settings
Messages setting for number of times to repeat an alert
iPad side switch setting to lock screen rotation or mute audio notifications and sound effects
Single tap conference call dialing with a pause to send a passcode
8. Bug fixes