If you are using macOS and want to reset PhpStorm to its default settings, you can use these commands (run them from a terminal):
rm -r -f ~/Library/Preferences/PhpStorm20.* rm -r -f ~/Library/Caches/PhpStorm20.* rm -r -f ~/Library/Application Support/PhpStorm20* rm -r -f ~/Library/Logs/PhpStorm20*
These commands remove configuration (in Preferences folder), caches (in Caches folder), plugins (in Application Support folder) and logs (in Logs folder).
More information can be found here.