Laravel updating multiple hasMany / belongsToMany relationships

I have inherited a project that has a a few CRUD forms … On the create form we need to create entries for a hasMany and belongsToMany relationship. So basically what i have got is the following

$movie = Movie::create($request->validated());

// Then to save the belongsToMany
foreach ($request['actors'] as $actor) {
  // do some data manipulation

  $actor = Actor::where('code', $actor->code)->first();

  $movie->actors()->attach($actor);
}

// Save the hasMany 
foreach ($request['comments'] as $comment) {
  // do some data manipulation

  $movie->comments()->create([
    'title' => $comment['title'],
    'body' => $comment['body'],
  ]);
}

I’m not sure if this is the best way of doing this, but it seems to work.

The problem I am having is that in the edit form, these actors / comments can be edited, added to or deleted and i am unsure of how to go about updating them. Is it possible to update them, or would it be better to delete the existing relationship data and re-add them?

I have never updated relationships, only added them so i am unsure how to even start.

Any help would be greatly appreciated.