How to swap projects under the same domain

Hi,

I have a website:

www. let’s call it project A .com

It has all the domain info (dns from google domains pointing to it) and is live.

But I’m now working on a new design (Project B) which has no domain assigned. Once it is finished, I would like to know how to replace Project A with Project B, under the same www. let’s call it Project A .com domain.

Thanks,

Daniel