composer upgrade to 2.0 code example
Example 1: upgrade composer version
composer self-update
Example 2: upgrade composer
To update composer command just find location of composer.phar and update as:
where composer
cd path_to_composer.phar
php composer.phar self-update
Example 3: 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