If you have a used Vita you may experience some problems with removing the old account attached to the system
I’ve recently bought a used PS Vita. Unfortunately the Vita’s previous owner forgot to format the Handheld and their data was locked onto the device, with no official clear instructions on how to remove them.
Step 1: Access Recovery Mode. With the handheld Power off, press and hold the PS Button, R Button and Power Button at the same time.
Step 2: Format the Memory Card. From the Recovery Mode Menu select Format Memory Card.
Step 3: Format the System. From the Recovery Mode Menu, select Restore PS Vita System.
Step 4: Vita will restart and prompt the initial setup. Enjoy.