Many situations are different, so step-by-step won’t always work for everybody. But in your case:
1) Create a Fully Hosted Domain here of your example.com (not devexample.com).
Make sure it’s under the same user as your dev example.com site so it will appear in the same home directory.
If you’re running your site here under WordPress, log into the wp-admin panel for Settings -> General and update the URL so it’s the new site URL. Then go to #2
2) FTP to your server here (dev example.com) and do some renaming:
example.com to old example.com, then dev example.com to example.com. So your dev domain will have your real domain name.
3) Go to Blogger, or wherever your domain is registered and update DNS so it’s using the DreamHost Nameservers.
It will take anywhere from minutes (not likely) to days (not likely), but probably hours before your new site replaces the old one in DNS. As soon as it goes live for you, hunt down any references to the Dev site and fix them in the configuration. In WordPress, some plugins will store the old Dev URL. Some posts and pages may include links to the old dev URL and will need to be re-edited.