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, from the Render Settings dialog, simply click to create on the Render Setting... button to create a new render setting:
Then select Corona in the Renderer drop-down list - this will load Corona with all the defaults restored:
You can always revert back to your changed settings by selecting the appropriate Render Settings option.