pip install vs apps in folder

[tech tech]

Hi, all,

I am interested in this project:
https://github.com/mbraak/django-file-form

I run "pip install django-file-form" and everything works fine.
But, I want to change some behaviors of this upload package.
I feel this link
https://github.com/mbraak/django-file-form/tree/master/django_file_form
has all the source code and I can change some code in this link.
However, after I run "pip uninstall django-file-form" does not work.
So, my question is why it does not work after I uninstall it.
I downloaded the whole software. Why doesn't the project use the
source of django-file-form in the folder?

Thanks,

Tom