migrate site question

I’ve transitioned a site before and it was pretty simple, but I can’t find the how-to on it now.

I have a site in a subfolder and I want to replace the existing HTML site with the WordPress one. Before I kept the folder in place, copied a few files, moved a couple others and that was that. It was in the codex somewhere, just a simple list of steps, and now I can’t find it.

any help would be appreciated.