First of all, always backup the wordpress folders and database before starting an upgrade.

Once done, you can take advantage of the build in upgrade link.

This usually gives timeout problems though:

• Download failed.: Operation timed out after 30 seconds
• Maximum execution time of 120 seconds exceeded

Here’s how to fix them:

• in wp-admin\includes\file.php increase timeout to 600 seconds
  $response = wp_remote_get($url, array(‘timeout’ => 600));
• At the end of wp-config.php add: set_time_limit (800);

That should do the trick!