How to flash Vanilla RootBox Jelly Bean 4.2.2 custom ROM for the Samsung Galaxy S3 I9300 device

1. Firstly download the Vanilla custom ROM from HERE and save this file on your PC, don’t extract its contents only save it.
2. Secondly download the Gapps compatible with Android 4.2.2 Jelly Bean OS from HEREand save it in your computer. This pack will install all the Google based applications.
3. Now, connect your S3 device to the PC using your USB cable.
4. Move the both downloaded files to your S3 device’s internal SD card without to extracting the archives components.
5. After you copied the files, disconnect the S3 device from the PC.
6. Power off your device and after that boot into CWM Recovery mode. To do that press the Volume Up+Home+Power buttons simultaneous and release the buttons when the CWM Recovery mode menu is fully displayed.
7. From the CWM Recovery menu select the ‘backup and restore’ option and chose to create a NANDROID backup of your actual ROM. This backup will represent a restore point in case you need to restore your actual ROM if your device won’t boot after you installed the Vanilla custom ROM.
8. From the CWM Recovery menu select ‘wipe data/ factory reset’ option, and after that confirm this action.
9. Now, select ‘install zip from sdcard’ and then ‘choose zip from sdcard’ and find the RootBox ROM copied zip file and confirm that you want to flash it.
10. After the Vanilla RootBox has been installed completely, you need to install the Gapp in your S3 device. To do that you need to select once again the “choose zip from sdcard’ option once again, find the copied Gapp zip file and after that install it.
11. Now, go back to the main menu of the CWM Recovery Mode and from there select ‘reboot system now’, this option will restart your smartphone.
12. Now you need to wait for completing the first boot process around of 6 minutes after your device will load the new custom ROM you need to join your Google account, and  now you can enjoy  your new Vanilla RootBox custom ROM installed in  your SGS 3 smartphone.
13. Congratulation, you successfully installed the new Android 4.2.2 Jelly Been ROM on your Samsung Galaxy S3 I9300.

Note: If, the new Vanilla RootBox custom ROM doesn’t work or you don’t like exceptionally well, you can restore your previous ROM using the NANDROID Backup that you have been created previously.