You can move the wp-content directory to a different location, which essentially renames it.
First, in your wp-config.php file, add this:
define( 'WP_CONTENT_DIR', $_SERVER['DOCUMENT_ROOT'] . '/folder/path/to/new/dir' );
And second, also in wp-config.php, add this:
define( 'WP_CONTENT_URL', 'http://yoursite.com/folder/path/to/new/dir');
You can read more about changing the wp-content dir on the Codex.