Step-1: Boot the Galaxy Grand Duos into recovery mode. To do so, first power off the phone and wait for five to 10 seconds until the device goes off completely. Press and hold Volume Up, Home and Power buttons together and release them once the Galaxy Note logo appears on the screen
Note: In recovery mode, use Volume keys to navigate up and down between options and Power button to select an option.
Step-2: Make a Nandroid Backup from the recovery. It is important, in case something goes wrong you can restore to the current status. To perform Nandroid Backup, go to Backup and Restore>> Backup
Step-3: Perform a Factory Reset (This will delete all apps and their settings and game progress). Select Wipe data/ Factory reset then select Yes on the next screen to confirm the action.
Step-4: Also perform System Format by navigating to Mount and Storage, select format/system then select Yes on the next screen to confirm the action
Step-5: In recovery mode, select Install zip>> Choose zip from sdcard (or external sdcard, where the files are saved). Then browse to the location where Android 4.4.1 KitKat CM11 ROM is saved. Select the ROM file and confirm installation
Step-6: After the ROM is installed, repeat the similar process to flash the Gapps file
Step-7: When the installation process is completed, return to the main recovery menu and reboot the phone by selecting Reboot system now
Note: If the device gets bootloop (gets stuck at logo while rebooting), perform afactory reset.
The Galaxy Grand Duos should now be updated with Android 4.4.1 Kitkat with CM11 custom firmware. Navigate to Settings>>About phone to verify the new software version of the Galaxy handset.