I am working on Laravel 5.4 with PHP version 5.6.4. My goal is to upgrade my project to Laravel 5.7 with PHP 7.1.
Now my question is: Do I have to upgrade to 5.5 > 5.6 >
There are some articles on documentation. You can upgrade to 5.7 directly but be sure to modify critical sections from this links 5.5->5.6, 5.6->5.7. And make a backup of current project first
Just update your laravel/framework dependency to 5.7.* in your composer.json file. Since you are upgrading from 5.4 to 5.7, then you can easily just run
composer update
And if you modified some of Laravel's Traits or Methods in your 5.4 application, then you can check here for more info