how to upgrade Composer 1 to Composer 2 code example

Example 1: upgrade composer version

composer self-update

Example 2: composer upgrade to 2

run which composer (output /usr/bin/composer)
run php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
run sudo php composer-setup.php --install-dir=/usr/bin --filename=composer