Spark 7.1 introduces the email verification out of the box. To prepare your application for the upgrade you need to add the following database field to your users' table.
$table->timestamp('email_verified_at')->nullable();
Spark 7.0 is a simple maintenance release to provide compatibility with Laravel 5.7. As such, there are no Spark specific upgrade instructions. You should simply upgrade your application using the Laravel 5.7 upgrade guide.