actualizar a versão do compositor
composer self-update
actualização do compositor do php
php composer.phar update
como actualizar o compositor em laravel
composer global require "laravel/installer:^4.0"
actualizar a versão global do laravel
FIRST METHOD :
===============
# uninstall the package
composer global remove laravel/installer
# reinstall
composer global require laravel/installer
SECOND METHOD :
================
Just upgraded from Laravel 7 to 8, and running
composer global require "laravel/installer:^4.0"
did the trick for me (i.e., without removeing first)