How to change data type and add column with migration without losing data? (laravel 5.3)

My migration is like this :

public function up()
{
    Schema::create('tests', function (Blueprint $table) {
        $table->increments('id_test');
        $table->string('name', 50);
        $table->timestamps();
        $table->softDeletes();
    });
}

public function down()
{
    Schema::drop('tests');
}

I want to change data type and add column in table test. Then update table in database. I edit like this :

public function up()
{
    Schema::create('tests', function (Blueprint $table) {
        $table->increments('id');
        $table->string('id_test', 18);
        $table->string('name', 50);
        $table->timestamps();
        $table->softDeletes();
    });
}

public function down()
{
    Schema::drop('tests');
}

Then I run : php artisan migrate:refresh

I lost my data in database

Is there any people who can help me?