Phone [Q] Samsung Galaxy S3 - How to remove root n back to original. Need Help!

Hi,

My Samsung GT-I9300 already root about almost a year. The problem is, i need back to original firmware.
i already forgot step to unroot back to original.

Current Baseband Version: I9300XXELKB.

my origin region is Malaysia.

before this im using odin and custom firmware. (if not mistaken).

im appriciate if anyone can help me. thanks.