iOS 10.3 is available for everyone to download right now. The update will roll out in waves, though, so if you've not got it just yet, don't panic, it should appear on your iPhone or iPad soon.
The original iOS 10 update rolled in September 2016, and since then we've seen upgrades to iOS 10.1, iOS 10.2 and now iOS 10.3.
To download and install iOS 10, you should see a message that an update is available. Before you begin you should make sure you back up your iPhone or iPad first.
How to download the latest iOS software
iPhone 5 or higher
iPad Mini 2 or higher
iPad 4th Gen or higher
iPod Touch 6th Gen
Next, make sure your device is plugged into a power supply, and that you're connected to a Wi-Fi network - as the download will be pretty big!
Open up the Settings app of your device and tap on 'General' then 'Software Update'. The iOS 10.3 update should then appear, and all you need to do is tap 'Download and Install'.
You can also choose to download the update later on when you're not using your device, as the iOS 10 update and installation process will make your iPhone or iPad unusable for a short while.
Tap 'Install Tonight' or 'Remind Me Later' to install iOS 10 at a more convenient time.
If you select 'Install Tonight' just plug in your iPhone or iPad into the power supply before you go to bed, and by the time you wake up iOS 10 will be ready and waiting for you.
Download and install iOS 10 from iTunes
You can also download and install iOS 10.3 through iTunes, which is a good choice if you do not have a reliable wireless connection.
To update to iOS 10.3 through iTunes, make sure you have the latest version of iTunes installed on your PC or Mac. Now connect your device to your computer and iTunes should open automatically.
With iTunes open, select your device then click 'Summary' then 'Check for Update'. The iOS 10 update should appear. When it does click 'Download and Update'.