You can publish or unpublish extensions at any time in two different locations:
Through the three-dot menu on the main dashboard
From the Options menu on the extension's configuration page
Extensions will show which state they're in on the configuration page, and in the admin bar at the top of the actual extension. This includes the following information:
When the extension was last published
If there are unpublished changes
If the extension is currently published or not
The Publish button is greyed out when there are no changes to be published.