Need help changing hdd on a 4.82 cfw and install 4.90 cfw

Hi guys I really need help, I just bought a ps3 today with 4.82 cfw Ferrox ( CECH 2004a). It has 120gb Im going to buy a 500gb hdd tommorow and since its a new hdd I want to install the 4.90 cfw, I watched both modded warfare an the mario guy videos. Nobody addresses the situation if Im on 4.82 or when putting a new hdd ( tbh its my fault I don't understand a thing (ofw hfw .....) Im lost).
Here is what I want to do : put a 500gb hdd and install 4.90 cfw.
What I dont understand...

Need help changing hdd on a 4.82 cfw and install 4.90 cfw