if i update laravel version to 7 what happens code example

Example 1: update php version in laravel

"config": {
    "platform": {
        "php": "7.0.7"
    },
    "preferred-install": "dist",
    "optimize-autoloader": true
}

run composer install

Example 2: laravel 7 upgrade

$>which composer
/usr/local/bin/composer

$>php -d memory_limit=512M /usr/local/bin/composer update
...