Easiest way will be to overload their default upload view.
If you look in the urls.py for the package it has two entries
path('image_upload/', views.image_upload, name='froala_editor_image_upload'),
path('file_upload/', views.file_upload, name='froala_editor_file_upload'),
Then create your own views doing what you want but serve them from the URL path that these would be on by default so that they are called instead.