I installed WordPress via Bitnami, and naturally proceeded to work with a child theme. But where are the files? Normally they should be in the same folder as WordPress. They are not. On Linux the path to these files is:
/opt/lampp/apps/htdocs/wordpress/wp-content/plugins
The directory is only for sudoers, så you may have to change the permissions to the folder, or edit as sudo / root. OS X may as well have to change permissions or work as the sudo.
On a linux system the quick and dirty solution is:
# sudo chmod -R 777 htdocs
On a Windows / OS X some bloggers suggest a rightclick - and then to give users read / write access. Then you're able to edit the files.