Update drupal 9

1. composer update (YES, simply run this command. That's good enough. It will update everything including core drupal 9.1.5.)
2. If this not works, then try the followings:
   
3. Update from web site:
   http://localhost/~chiao/drupal9/web/update.php 
   
4. cd public_html/drupal9, then issue the following commands:
   
1. Put drupal site into maintenance  mode
   
2. composer outdated 'drupal/*'
3.  composer update drupal/core 'drupal/core-*' --with-all-dependencies