Update from Laravel 5.5 to 6

I am trying to update the Laravel5.5 project to 6. What I tried is first describing the package update

"php": "^7.2",
"ext-SimpleXML": "^7.3",
"barryvdh/laravel-ide-helper": "^2.6",
"doctrine/dbal": "^2.10",
"fideloper/proxy": "^4.0",
"jeroennoten/laravel-adminlte": "^2.0",
"laravel/framework": "^6.0",
"laravel/tinker": "~1.0",
"laravelcollective/html": "^6.0",
"maatwebsite/excel": "^3.1",
"laravel/ui": "^1.1",
"phpoffice/phpspreadsheet": "^1.9",
"phpoffice/phpexcel": "dev-master"

next

composer update

I get error

Call to undefined function str_slug()

So install this library

composer require laravel/helpers

Then this error came out

JeroenNoten \ LaravelAdminLte \ ServiceProvider :: class, not found

Reinstalling adminLTE doesn't help, commenting out and reinstalling doesn't work, I'm stuck and want help

I need help

via Chebli Mohamed