How to reset settings to their default values?
It is fun to experiment with Corona's settings, but after some time spent fiddling with them, you would probably like to get back to their defaults. To do this, simply right-click on each setting's spinner and instead of resetting itself to 0, it will revert to the default value.
To reset all Corona settings to their defaults, go to Render Setup > Scene > Reset settings.
Note: if you haven't saved your custom settings, it won't be possible to undo this!