Reflecting Changes into ERPNext Instance when custom app code is modified

Hyy community,

I have before_install hooks when someone install my app changes are getting into there instance but when I make changes into my custom app and push the changes into GitHub,

  1. It is not bringing changes to their ERPNext Instance even after migrating the site.
  2. Not deleting the custom app configuration even after dropping the app from the site.

Can anyone give some insight how these can be tackled. Thank You