Go to the PlayStation Account Management site and log in. In left menu, click “Security.” At the bottom of “Security” section, click on the [Sign Out of All Devices] button. Click “Ok” to verify your decision.
Forum discussion at Reddit.
You will now have three options: username, password, and email address.
You can type in a new username if you want to create an entirely different account, or you can log out of this account for the time being by clicking on “log out”.
To delete your current profile permanently from the app so that no one else can access it without creating their own profile also, select “Delete user” and verify your decision.
To link or unlink your account, select (Settings) > [Account] > [Link with Other Services]. This option is available only for adult accounts.
To deactivate a PlayStation 4 from the console select ‘Settings’ then ‘Account Management’, go down to activate as your primary PS4. Choose Deactivate and confirm your decision.