Unlocking a Verizon cellphone security code depends largely on the phone's brand and model. On a Motorola Verizon phone, click the OK button, press the Navigation button and scroll down to select System. Select Security, and then New Passwords and then Security Code.
The old security code is necessary to unlock or change the phone's security code. If there is no old security code, the default may be the last four digits of the phone's telephone number, 1234 or all zeros. Enter the old security code and then the new desired code. It may be necessary to confirm the new security code by entering it a second time before it is usable.