Clean-Up Deleted Users and Storage

I would like to be able to delete my many InActive Directory Users.  But I don't dare because they have stored files and I don't know if they are shared and are being used by other users.

I could save a lot of storage space and clean our a lot of users if I could do that.

Will you please make it possible for me to see InActive User data better and know if it is being shared with other users?

My Org ID is:  F7D9D36B545A4A780A4C98A7