Do I need to manually wipe my device completely before installing this Rom or Rom itself will automatically wipe my device while installing? Is it the same process of installing??
Copy the ROM file to your Galaxy S3's internal SD card.
Turn off your Galaxy S3.
Boot into Recovery Mode by pressing and holding down the Volume Up, Home, and Power buttons.
Make a NANDroid Backup by selecting Backup and Restore. Select Backup.
Select Wipe Data/Factory Reset. Confirm the action on the next screen.
Select Install ZIP from SD card.
Select Choose ZIP from SD card and then select the ROM file.
Follow the on-screen instructions.
Select Reboot System Now.