Is it easy migrade to 3.8 or 4.x CakePHP? Or start from scratch on new install CakePHP 4.x

I have some old coded Sites from mid-2016, CakePHP 3.1.4 / 3.1.6 / 3.2
well running on PHP 7.0 and MySQL 5.6 // deprecated

I tried to run on PHP 7.1 but failed…
Can these run on MySQL 5.7…?

What is the easier thing I can do for these sites???
Is it easy to migrate to 3.8 or 4.x CakePHP??? Or start from scratch on new install CakePHP 4.x and recreate them???