How to upgrade laravel 5.5.32 to 5.6

Below is my composer.json

{
	"name": "laravel/laravel",
	"description": "Laravel Ecommerce",
	"keywords": ["framework", "laravel"],
	"license": "MIT",
	"type": "project",
	"require": {
		"php": ">=7.1.3",
		"laravel/framework": "5.6",
		"backpack/base": "^0.8.0",
		"backpack/crud": "^3.3.0",
		"backpack/settings": "^2.0",
		"backpack/permissionmanager": "^2.1"
	},
	"require-dev": {
		"fzaninotto/faker": "~1.4",
		"mockery/mockery": "0.9.*",
		"phpunit/phpunit": "~7.0",
		"symfony/css-selector": "3.1.*",
		"symfony/dom-crawler": "3.1.*",
		"laracasts/generators": "dev-master as 1.1.4",
		"backpack/generators": "^1.1",
		"filp/whoops": "~2.0"
	},
	"autoload": {
		"classmap": [
			"database"
		],
		"psr-4": {
			"App\": "app/"
		},
		"files": [
			"app/Http/helpers.php"
		]
	},
	"autoload-dev": {
		"classmap": [
			"tests/TestCase.php"
		]
	},
	"scripts": {
		"post-root-package-install": [
			"php -r \"file_exists('.env') || copy('.env.example', '.env');\""
		],
		"post-create-project-cmd": [
			"php artisan key:generate"
		],
		"post-install-cmd": [
			"Illuminate\Foundation\ComposerScripts::postInstall",
			"php artisan optimize"
		],
		"post-update-cmd": [
			"Illuminate\Foundation\ComposerScripts::postUpdate",
			"php artisan optimize"
		],
		"post-autoload-dump": [
			"Illuminate\Foundation\ComposerScripts::postAutoloadDump",
			"@php artisan package:discover"
		]
	},
	"config": {
		"preferred-install": "dist"
	}
}