This was a question posted in a marketing forum:

Ok. I’m a WP dunce but it’s clear it’s something I want to be using
now. Basic questions I could research and figure-out, but here I
can just ask.

1. Can I develop a WP site in a subdomain and then easily move it
once it doesn’t suck to a prefered domain?

(of course I can. I know I can just copy the files in the subdomain
folder. The real question is: do I have to copy and finagle with the
darned database, or can I just have the “new” site – in the top-level
domain – just query from the same database?)

I could spend an hour figuring this out of course. I think I should be
able to do this easily but I’m not quite sure which “end” to approach
it from so I don’t wind-up with a duplicate site that doesn’t work the
same as the original.

Fix from the codex

Here’s the solution in video format from my blogging techniques site called quickwordpress.com