1.- Enable Uninstall mode
Go to WIRIS filter - Maths settings and enable uninstall mode.
2.- Uninstall WIRIS filter
Once uninstall mode has been enabled, WIRIS filter can be uninstalled from general filter settings.
3.- Uninstall WIRIS editor plugin
Go to editor settings (Atto or TinyMCE or both) and unistall WIRIS plugin.