upgrade to a newer watch
how to upgrade from apple watch series 6 to apple watch series 8
Question marked as
Go to Apple web store (or physical high street store if nearby) and decide which watch you want. Make Purchase and pair/set up in the Watch app of your iPhone. User the same Apple ID as your iPhone and existing Apple Watch.
You can have more than one watch paired to your iPhone, you simply need to tell it which one you are wearing when you change.
Use more than one Apple Watch with your iPhone - Apple Support
If you plan to sell or recycle your old watch to a family member, please also see What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else - Apple Support