Building wp on .net want urls to be .com

I am building a wp site on the newsite.NET domain.
When finished we want to point the newsite.COM domain name to this same site. I know how to point the nameservers.

What I need is directions on how to then have the urls on the .NET site change to .COM.

As far as WP is concerned, nothing is moving.
The site does and will have a lot of photo images and mp3s, and inner linking. The string will be the same length.

So what is the best way to do this?

Thanks