Authorisation and Deauthorisation ONLY applies to Computers...
If you no longer have, or access to, the computer(s) you want to deauthorise,
Log in to iTunes, go to "view your account info" on the itunes store, deauthorise all five,
(Please Note: this can only be done Once every 12 months).
Then re-authorize your current Computer(s) one at a time.
Authorise / Deauthorise About