Well first off if you want to downgrade it you need an e3 flasher or progskeet (not recommend requires alot of soldering) and when you have that you can follow my guide here (The Video is for the fat and the text guide is for the slim) https://www.mpgh.net/forum/showthread.php?t=893503
It allows you to downgrade ps3 just an fyi make sure you have a HDD dock that supports ESATA as your ps3 hdd will be connected externally since the e3 flasher is connected threw the HDD space