Hi Keith. You must be eligible to the following to be able to unlock your phone:
- The device must be a T-Mobile device.
- The device must not be reported as lost, stolen or blocked to T-Mobile.
- The account associated with the device must not be cancelled and is in good standing.
- You have requested no more than 2 mobile device unlock codes per line of service in the last 12 months.
- The device must satisfy all the Postpaid or Pay in Advance (Prepaid) Unlocking terms outlined below.
- T-Mobile may request proof of purchase or additional information in its discretion and certain other exceptions may apply.

If you are eligible, please contact T-Mobile for unlocking.(source)

You have to pay your carrier for the unlock code. Which carrier are you with? I'll help you find out how much it would cost to unlock your phone.