.I flashed the 681 ftf and was going to update to 757 to root but the pc said it could not recognize the modified firmware. Do I need to relock bootloader to do an update to 757?
Did a little test myself and yes you do need BL locked for the OTA updates else download the TFT as suggested above ^^. .681 and .757 difference only 10mb so it is pointless to redownload the whole tft so what i did was relock the bootloader to update it. Make sure you are using the stock kernel