Uninstall plugin | WordPress.org

Good morning, I installed your plugin maintenance ver. 3.6.1 on wordpress
When I turn it on it works perfectly,
but when I turn it off the site remains in maintenance without the image and with the writing
Briefly unavailable for scheduled maintenance. Check back in a minute.
Even if I turn it off it remains in maintenance mode
How do I uninstall it?

The page I need help with: [log in to see the link]