lts

Update Composer.json

tukar dependencies framework 5.4 kepada 5.5 

"require": {
        "php": ">=5.6.4",
        "laravel/framework": "5.5.*", //<-- tukar drpd 5.4.*
        "laravel/tinker": "~1.0"
    },

tukar php unit 5.6 kepada 5.7

"require-dev": {
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "0.9.*",
        "phpunit/phpunit": "~5.7"//<-- tukar daripada 5.6
    },

run composer update

composer update

Boleh refer

https://laravel.com/docs/5.5/upgrade

https://laracasts.com/discuss/channels/laravel/upgrading-to-55-from-51