To update your W9 in Liquid, you'll need to ask your Client to send you a new onboarding process. When you complete that onboarding process, you'll complete a new W9 form.
If the existing Master Contract should stay in effect (and they don't need you to sign a new contract), your Client can download the Master Contract and use the Offline Contracts onboarding process to re-onboard you.
If your business name has changed, you will likely want to have them send you new contracts to sign under your new business name.
When you accept the new onboarding process, make sure to do so while logged in to your existing Liquid account and select your existing business.