OK...that other post got deleted or changed...but was nothing to do with this.
What you need to do is change theme to Clean theme, and then remove Essential from your server using...
Site Administration > Plugins > Plugins overview
Scroll to the bottom of that page and find the Essential theme and Uninstall it. This deletes the settings related to this theme but you may have to remove the theme manually when prompted.
Then get a new updated version and install it.
https://github.com/moodleman/moodle-theme_elegance/archive/master.zip