Root composer.json requires friendsofphp/php-cs-fixer ~2.14.0 -> satisfiable by friendsofphp/php-cs-fixer[v2.14.0 …

solution :

• run this command composer require magento/composer-root-update-plugin=~1.0 --no-update
• open composer.json and change riendsofphp/php-cs-fixer from ‘~2.xx.x’ to ‘~2.16.0’
• execute this command ‘composer update’

Root composer.json requires allure-framework/allure-phpunit ~1.2.0 -> satisfiable by allure-framework/allure-phpunit[1.2.0 …

• open composer.json and change allure-framework/allure-phpunit from ‘~1.2.0’ to ‘~1.4.0’
• execute this command ‘composer update’

What is easiest way to upgrade Magento

download a new and fresh Magento
copy composer.json to your old project
move your old composer.json repositories and packages to new composer.json
composer update