This won't be super in depth from me, but follow this link I attach. The first post has installation instructions. Follow them to get the latest custom recovery and MJ9 firmware before you flash the rom. I link to this rom since it is one of the more closer roms related to stock 4.3.
In a nutshell, and as long as you have an unlocked bootloader (custom recovery like twrp or cwm), you have to Odin the latest firmware (see link) and then flash the rom afterwards.
Remember, if you already took the over the air update to 4.3, you're done flashing.
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