Not sure if I'm thinking of this in a more complicated way than is necessary. What I want to do is very simple, but I couldn't find anyone else with a similar question (apologies if it was staring me right in the face!).
Here's what I want to do:
I have existing site at, let's say, www.existingsite.com.
I want to start a new site at, say, www.testing.existingsite.com, using Wordpress, so I'll be installing Wordpress there.
Then, after having the two sites run side-by-side for a while, I want to replace the stuff at www.existingsite.com with the stuff at www.testing.existingsite.com.
How do I do that?