t-mobile S3 with AT&T firmware

[Hassler Osorto]

Hi i bought my Samsung Galaxy S3 used in the back says T-Mobile but my phone has the custom apps from the carrier and they are from AT&T so i was wondering if thats the reason that i cant update my phone to android 4.3 or 4.4? (my samsung is currently with Android Jelly Bean 4.1.2). I found like the file to make the manually update installing it from the sd card on Recovery Mode but i was wondering what would happend if i install it? Oh and someone could tell what someone did to the phone(from t-mobile) so that it has an at&t firmware?

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