I want to update my watch

See -> Update your Apple Watch

Update your Apple Watch – Apple Support (UK)

• Leave your Apple Watch on its charger while it's updating. Don't restart your iPhone or Apple Watch, and don't close the Apple Watch app. When the update has completed, your Apple Watch will restart on its own.

See the following Apple articles:

Set up your Apple Watch -> Set up your Apple Watch – Apple Support (UK)

The Apple Watch app -> The Apple Watch app – Apple Support (UK)

Apple Watch user guide -> https://books.apple.com/book/id6442854652

Apple Watch Support -> Apple Watch - Official Apple Support