Instructions
Turn on your PSP Go and let the XMB menu load.
Select "PlayStation Network" and then "Account Management." Wait for the unit to connect to PSN.
Scroll down to "System Activation" and select "Deactivate." You will need to do this in both the "Video/Comics" folder and the "Games" folder. Deactivating your account prevents you from being unable to connect to a new device, as your PSN account only supports five devices total.
Head back to the XMB menu and choose "Settings." Open the "System Settings Menu" and navigate to "Format System Storage."
Select "Yes" on both confirmation prompts to completely wipe your PSP Go's flash memory. You can also wipe external memory cards through the "Format Memory Stick" menu.
Go back to the XMB again and select "Settings," then "System Settings."
Click "Restore Default Settings" and confirm by pressing X. Restart your PSP Go once complete. When the device starts up, all of your personal information and settings will be gone.