How to fully remove an external library in a project?

Maybe You have to go:

right click on your project:

properties > select "Android"

Under "Library", remove the library you want.

It maybe some libraries include other libraries so you couldn't remove it from where you have tried.

Right click on the jar file -> Build Path -> Remove from Build Path

Open settings.gradle and delete:

"include ':librayname'"

Then delete lib file from app Myproject/app folder.