There’s a maintenance mode plugin installed on your site. To activate the maintenance mode, click on Maintenance Mode under the Settings tab. Then, select the Activated box, set a time to notify readers when your site will return to normal production, and click Save.
When your site is in maintenance mode, people with user accounts will still be able to log in to the site by clicking the link in the bottom right of the site.
Don’t forget to remove the maintenance mode when you are finished — you must click the Deactivate link and click Save to do this.