cannot update iwork for used perchused mac air
i perchused used mac air with pre-installed iwork. i have 2 versions of iwork apps. one older than the other, both are running & working. i cannot update any of them.
when i receive updates available from apps store, i cannot update because it need the apple id of the old owner. if i change the requested id using mine, updates fails
any one can help
thx
MacBook Air, OS X El Capitan (10.11.4)