customization – How do I make mysite.com/comingsoon WordPress to become my main website’s WordPress?

I joined Bluehost and then I can create some WordPress, except if it is the button “Start Designing”, I cannot make it the top level, root of the website.

If I want to add to top level website, I have to use “No thanks, go to WordPress”.

So I created a /comingsoon instead, and that will let me choose some designs.

The tech support person said, I can just

cd ~/public_html
cp -R comingsoon/* .
rm index.html.  # if any

But that’s a really low level operation. It didn’t work initially and he said he had to do something related to Weebly. How does it work? How do I make the mysite.com/comingsoon content to become mysite.com ?