You mean remove them from the online account page? That would have happened automatically had the suite been uninstalled from each machine in the normal way, via Control Panel, however as that is probably not possible, simply call Customer Service and have them do it for you.
The link is under Useful Links at the top of this page.
If McAfee was already removed on the discarded computers the license status normally change to Inactive from Active status , so you should have 2 licenses spare to install the McAfee in other computers. But anyways you can call the customer service suggested by peter to confirm it.