You can activate one PlayStation 4 system as the primary PS4 for your account. Watch this video for activation instructions and to learn about the benefits of primary PS4 system activation.
Sign in on http://www.playstation.com/account to manage the devices that are activated for your PSN account. There is an option to deactivate all devices for your account, but it can only be used once every six months. Check this article for updated instructions for deactivating all devices for your account: https://support.playstation.com/s/article/Deactivate-PlayStation-Consoles-Via-Website?language=en_US
Source: Playstation YouTube
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