There are several steps when wanting to upgrade your CiviCRM install on WordPress. The official guide is here:
https://docs.civicrm.org/sysadmin/en/latest/upgrade/wordpress/

This is my simplified quick steps that work for me…

(1) Open browser and login to your CiviCRM install. Keep browser open during this entire process.

(2) Download most recent version of CiviCRM https://civicrm.org/download for WordPress onto your computer, and extract the civicrm folder from the zip/tar file.

(3) On your server, rename the /wp-content/plugins/civicrm folder to /wp-content/plugins/civicrmOLD

(4) On your server, move the /wp-content/plugins/civicrmOLD to /wp-content/civicrmOLD

(5) Upload the civicrm folder from your computer to your server into the /wp-content/plugins/ directory.

(6) Delete all the files in /wp-content/uploads/cicvcrm/templates_c/ directory.

(7) From browser, go to http://example.org/wp-admin/admin.php?page=CiviCRM&q=civicrm/upgrade&reset=1 to start the database upgrade.

(8) After complete, check that CivicCRM is working properly, and if it is you can then delete /wp-content/civicrmOLD folder and files.