Index: src/wp-admin/includes/class-wp-upgrader.php
===================================================================
--- src/wp-admin/includes/class-wp-upgrader.php	(revision 27241)
+++ src/wp-admin/includes/class-wp-upgrader.php	(working copy)
@@ -52,6 +52,7 @@
 		$this->strings['installing_package'] = __('Installing the latest version…');
 		$this->strings['no_files'] = __('The package contains no files.');
 		$this->strings['folder_exists'] = __('Destination folder already exists.');
+		$this->strings['remove_first'] = __( 'Unable to install over existing folder - you probably need either to delete the installed version first, or to perform your update using the dashboard\'s updates page.' );
 		$this->strings['mkdir_failed'] = __('Could not create directory.');
 		$this->strings['incompatible_archive'] = __('The package could not be installed.');
 
@@ -364,6 +365,9 @@
 		$this->skin->set_result($result);
 		if ( is_wp_error($result) ) {
 			$this->skin->error($result);
+			if ( in_array( 'folder_exists', $result->get_error_codes() ) ){
+				$this->skin->feedback( 'remove_first' );
+			}
 			$this->skin->feedback('process_failed');
 		} else {
 			//Install Succeeded