locked account set as primary

I recenly purchesed a second hand playstation 4 and when i got it it already had a account on the ps4 and the account was set as primary for the playstation.  I tried to deactivate it but i needed the account password and the owner before me does not know the password or email for the account.  is there anyway that i can get the account off my ps4 or that i can deactivate the account without having to sign into the account?  I am willing to completely reset the ps4 if that is even possible. Please someone help!