In most cases, you don't need to do anything to upgrade, the API has remained the same.
The facade has been moved from Spatie\Fractal\FractalFacade to Spatie\Fractal\Facades\Fractal.
If you have a configuration file named laravel-fractal.php, rename it to fractal.php for it to still be used.
v2 has mainly been made to provide compatibility with fractal 0.16 through fractalistic 2. In that version of Fractal your transformers, includes and excludes should return an array. String, ints, bools and such are not allowed anymore.
If all your transformers follow that rule you should be able to upgrade to v2 without any modifications to your code.