I use ssh to edit all my files but it is possible that access via WordPress itself might be useful sometimes. For example to give ad-hoc access to another developer.
From Bitnami docs on how to edit WordPress files,
How to edit the WordPress files?
For security reasons, WordPress files are not editable from the WordPress application itself [using WordPress’ built in Theme Editor]. If you are using a Virtual Machine or a Cloud Image, we would suggest to use a FTP client to edit the files remotely.
Another option is to change the permissions to be able to edit from the WordPress application temporary. Note that this configuration is not secure so please revert it after editing the files temporarily:
$ sudo chown -R daemon:daemon /opt/bitnami/apps/wordpress/htdocs
To revert this change you can run the following command:
$ sudo chown -R bitnami:daemon /opt/bitnami/apps/wordpress/htdocs
[I have put in the missing -R option to set this recursively down the whole tree – James]