Composer 2.0 is now available and you should upgrade. See https://getcomposer.org/2 code example

Example: upgrade composer

To update composer command just find location of composer.phar and update as:
 where composer 	#Retrieves you location of your composer.phar
 cd path_to_composer.phar #Move to directory with composer.phar
 php composer.phar self-update	#Update your composer