If you're on Metro PCS, just ask for them to unlock it.
I'm guessing you have the phone paid for.
Even then, you have to have Metro service for three months before they'll unlock it.
Reason is, the phone is sold below value vs the postpaid, so, they can recoup the subsidy & at minimum, break even.
Google is your friend for getting an
unlock code that'll work with the Device Unlock app, but, it's not free, probably more than you're willing to pay, considering the cost of the phone.
The most painful less/less expensive path to unlock this phone is just meet Metro's
service terms & get the unlock free.
EDIT:
Upon further review, I see this is not a MetroPCS phone, so, the above definitely doesn't apply.
Sorry I couldn't be of more assistance, but, I'd imagine once the phone is paid for, you should be able to get it SIM unlocked.