Step 1:
$ drush archive-dump
Database dump saved to /tmp/drush_tmp_1533355712_5b6526c0c36ca/drupal_8_5_2.sql                              [success]
Archive saved to /Users/anisur/drush-backups/archive-dump/20180804040823/drupal_8_5_2.20180804_040824.tar.gz [ok]
/Users/anisur/drush-backups/archive-dump/20180804040823/drupal_8_5_2.20180804_040824.tar.gz

Step 2:
$ drush ups
Checking available update data ...                                                                           [ok]
Checking available update data for Drupal.                                                                   [ok]
 Name    Installed Version  Proposed version  Message                   
 Drupal  8.5.2              8.5.6             SECURITY UPDATE available 

Step 3:
$ drush sset system.maintenance_mode 1

Step 4:
$ drush cr
Cache rebuild complete.   

Step 5:
$ drush up drupal
Update information last refreshed: Sat, 08/04/2018 - 00:17
 Name    Installed Version  Proposed version  Message                   
 Drupal  8.5.2              8.5.6             SECURITY UPDATE available 


Code updates will be made to drupal core.
WARNING:  Updating core will discard any modifications made to Drupal core files, most noteworthy among these are .htaccess and robots.txt.  If you have made any modifications to these files, please back them up before updating so that you can re-create your modifications in the updated version of the file.
Note: Updating core can potentially break your site. It is NOT recommended to update production sites without prior testing.

Do you really want to continue? (y/n): y
Project drupal was updated successfully. Installed version is now 8.5.6.
Backups were saved into the directory /Users/anisur/drush-backups/drupal_8_5_2/20180804041729/drupal.        [ok]
No database updates required                    

Step 6:
$ drush updb
No database updates required       

Step 7:
$ drush sset system.maintenance_mode 0

Step 8:
$ drush cr
Cache rebuild complete.