To upgrade drupal 7 with latest version, you need to follow the simple steps:--

1. Keep the backup of database and Drupal files.
2. Download latest version of Drupal 7 and extract it.
3. Remove "sites" folder from downloaded files.
4. Remove htaccess and robots.txt file from downloaded files(if any modification done in old files).
5. Put site in Maintenance mode.

   

   Go to Administration > Configuration > Development > Maintenance mode. Enable the checkbox "Put site into maintenance mode" and save configuration.

6. Upload your latest Drupal files on server in order to replace all files(except "sites", htaccess and robots.txt).
7. Once all files are uploaded then Run update.php by navigating http://example.com/update.php(replace example.com with your domain name). This will update the core database tables.

   

   If you are unable to access update.php do the following:
   • Open settings.php with a text editor.
   • Find the line that says:

     $update_free_access = FALSE;

   • Change it into:

     $update_free_access = TRUE;

   • Once the upgrade is done, $update_free_access must be reverted to FALSE.
8. Go to Administration > Reports > Status report. Verify that everything is working as expected.
9. Go to Administration > Configuration > Development > Maintenance mode.

   

   Disabled the checkbox "Put site into maintenance mode" and save configuration.