Unfortunately since you are still under contract you have a legal obligation to AT&T. We can't offer you a link that will be in violation of the contract you signed. The correct way to proceed is to pay off the contract as stated in the link below.

AT&T requirements:
https://www.att.com/deviceunlock/#/


Here is the AT&T online unlock tool:
http://www.att.com/esupport/article.html#!/wireless/KM1008728