I am unable to change any LDAP settings. They're all greyed out.

This means that PHP LDAP module is not enabled. Follow these steps to enable it:

1. Check the "ext" directory where PHP extensions are stored. There should be the php_ldap.dll file. If it doesn't exist you should run PHP installation and add this module.
2. Open the php.ini configuration file and find following line there:
   
   ;extension=php_ldap.dll
3. Uncomment it, or if there is no such a line, just add the following one:
   
   extension=php_ldap.dll
4. Restart your web server.