You have your WordPress site setup for some domain, such as mysite.com.
Now you want to change that domain to sitenew.com. How do you do that?
On a regular, single-site install (which is what most WordPress sites are), on the left side of your dashboard there is a Settings menu. Find “General” in there and click on it.
Then there are two boxes:
WordPress Address (URL)
Site Address (URL)
Change those to your new domain sitenew.com and click Save.
That’s it. 🙂