I have a site but need to do a whole revamp. I want to see what it is like befor

Hi all.

I have searched and found similar questions but nothing the same and certainly not an answer that I understand. I am very very new to wordpress and do not really understand it.

I have a site already up and running that I have inherited in my new job. My boss wants to change the whole site – a new theme and content.
We don’t sell anything other than a service and we will not be using the blogging facility.

I need to set the site up as if it was published on the web so she can check she likes it all before I switch over to it.

Could anyone explain in REALLY EASY terms how to do this?

Many thanks