If you need to change the Disqus shortname being used on your WordPress site, you'll need to reset the Disqus plugin.
- login in as admin for your WordPress site
- click on "Comments" in the admin sidebar
- choose "Disqus"
- click "Plugin Settings" in the upper right corner
- scroll down to the bottom of the plugin settings page
- click the "Reset" button under "Reset Disqus"
- click "reinstall"
- login with your primary moderator credentials
- choose your preferred shortname from the list
Tip: If you encounter an error that says you must upgrade your database to continue, click "Upgrade" and continue – you will need to click "Reset" again