Cool [Q] Omega Rom v9 to v21.1 please help!

Hi all, thanks for reading.

Have not upgraded/flashed for quite some time.

I currently have Omega Rom v9 using 4.2.2
Wanting to upgrade to v19 on 4.3
Or v21.1 on 4.4.2

Is there anything I must know before doing this?

Do I download bootloader, modem and then flash with v21.1? Or I need something else?

Thank you for your time!