It is absolutely essential that you perform a full backup of all your apps, data and settings before attempting a flashing procedure. Additionally, it is recommended to make backups of your /efs and /persist partitions which among other things contain your IMEI. In rare cases you might destroy these during flashing and you will have no way of getting them back. Your carrier will most likely not allow you to connect to it without a valid IMEI. A backup can be performed using adb like this: adb shell su -c "dd if=/dev/block/mmcblk0p27 of=/sdcard/efs.ext4 bs=4096" adb shell su -c "dd if=/dev/block/mmcblk0p12 of=/sdcard/persist.ext4 bs=4096" Flashing your phone voids your warranty. In the event that you need to have your phone repaired under warranty, you will have to flash it using the firmware it initially shipped with. If this is your first time flashing, it is therefore advisable to write down the original PDA, CSC and PHONE IDs that your phone shipped with. "Dial" the number *#1234# and write down the three ID strings. These exact three ROM parts can then be restored by downloading the appropriate stock firmware from sammobile.com.