“Service Temporarily Unavailable
The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.”
If you are getting a service temporarily available error on your Magento store after performing some update on the extensions or theme area, you can try to fix it using file manager. During maintenance, Magento creates a file named Maintenance.flag which is removed after the completion of the update process. In case if there is any error and the updated did not went right, the file may not be removed automatically and thus send the store to a state of error.
In this case you can check if there is a file called maintenance.flag in your Magento installation directory. If there, delete it and your site should be up again.