The introduction of Angular 2 meant big changes for Angular developers. Often the best thing to do is to undertake a rewrite of the app, module by module.
You can learn how to get started in this video tutorial from my course Upgrade Your App to Angular 2, in which you’ll learn how to set your project up for Angular 2.
The full course, Upgrade Your App to Angular 2, takes you through the full process of taking a simple Angular 1 app and upgrading it to use Angular 2. You'll see how each concept and structure in Angular 1 translates to the new version. After viewing this course, you'll have a better understanding of how to migrate your apps to Angular 2.