You also need to deactivate the system.
HOW TO ACTIVATE/DEACTIVATE A SYSTEM (AS OF V2.10):
(Please Note: If 4 or less systems have been activated, the next system that downloads purchased content will be AUTOMATICALLY ACTIVATED)
1. Go to PLAYSTATION Network icon in the XMB.
2. Go to Account Management and press X.
3. In the Account Management screen, go to Account Management and press X.
4. In the Account Management screen, go to Activate System and press X.
5. In the Activate System screen, go to PLAYSTATION3 (This system) and press X.
6. In this panel, it will show you whether or not your system is activated. If it is not activated, you can activate it by pressing X on the ACTIVATE SYSTEM option or, if it is activated, you can deactivated by pressing X on the DEACTIVATE SYSTEM option.