New to Studio -- how to upgrade client site?

I’m designing a site for a client using the new Wix Studio … which is my first time using it.

What exactly is the “right” way to upgrade?
I have created the page using wix studio, do I personally upgrade the site to a premium plan and then charge the client for that cost? Can i have the client input their payment information on the billing? The client has already purchased the domain elsewhere previously

Product:
[ Wix Studio Editor]

What are you trying to achieve:
I’m just looking for information… there’s so much on Wix Studio I just dont seem to understand any of it