RENE RITCHIE . https://www.imore.com/how-download-watchos
1. Update your iPhone to iOS 11 or later.
2. Connect your iPhone to Wi-Fi and launch the iOS 11 Watch app.
3. Make sure your Apple Watch is charged to at least 50% and connect it to the magnetic charger.
4. Tap on the My Watch tab.
5. Tap on General.
6. Tap on Software Update.
7. Tap on Download and Install.
8. Enter your iPhone Passcode when prompted.
9. Tap Agree to the Terms and Conditions.
10. Tap Proceed on your Apple Watch to begin the download.
11. Enter your Passcode on Apple Watch.
The watchOS 4 update will download and transfer to your Apple Watch and Apple Watch will reboot to apply the update. You can follow the progress on the Apple Watch screen, and once it's done, you'll be all set.