This phone has already received to major updates, that are, Nougat and Oreo. Samsung provides only two major OS updates to J-series phones. So J7 Prime is not expected to get updated to Android Pie. You can try flashing a custom ROM based on Pie. Search on XDA developers website to find a compatible ROM and steps to install it. Samsung has posted which phones are set to get Pie in an article available on Samsung Members app's Notice section. Check the list if you would consider upgrading to one of those phones.