This link has instructions to upgrade from 5.7 to 5.8.0. If you want to upgrade to a different version, select the appropriate version on the upgrade guide
https://laravel.com/docs/5.8/upgrade

Update your laravel/framework dependency to 5.8.* in your composer.json file
Next update third party dependencies. From your project folder run:

    composer update

If you are using any of the backward incompatible methods listed in the upgrade guide, make the changes to your application
https://laravel.com/docs/5.8/upgrade

This command generates a migration file (test_migration_file in this example) under database/migrations. The filename you specify will be prefixed with a date and timestamp ( HH_MM_SS_nnnnnn_test_migration_file)

php artisan make:migration test_migration_file

Laravel framework version

php artisan --version