Normally you have folder browsing disabled for your site, so a user would not be able to access that folder directly to do anything anyways. PHP files are also read and served by the server not directly as text so a user can't see the contents of a PHP file either.
If you can get to that folder from your desktop via a browser then you need to setup a bit more security on your site via your hosting admin control panel. If you're not sure what you're doing then you can also send an email to your support for assistance.
If you rename that folder then I'm pretty sure your site will quit working.
