Ctrl + G to create group, Shift+A->Collection Instance to create, how to edit the group instance?

Ok so Control + G to create group, and Shift+A->Collection Instance to create instance, fine, how do you edit the group instance if the original one is deleted from the viewport ?

How do you remove the group instance from the file because even after all existence of it is removed from the viewport, you can still see it in Shift+A->Collection Instance.

How do you make the created instance unique [wouldn’t be affected if original change] ?