What documention for File upload?

What docs are there that show the processing of file upload?

I have created the form using the docs at https://doc.nette.org/en/forms

And I can see the API at https://api.nette.org/…eUpload.html

But, how do I access the API to process the form?
Eg:

<?php
$form->addUpload('hero', 'Hero Image:')
     ->setRequired('Please select a Hero Image.')
     ->addRule(Form::IMAGE, 'Thumbnail must be JPEG, PNG or GIF')
     ->addRule(Form::MAX_FILE_SIZE, 'Maximum file size is 1Mb.', 1024 * 1024);
?>

So, in the formSucceed function, how is the hero image accessed?