It depends since some of those models can and cant be downgraded what is the data code of the console... I've created a thread
You must login or register to view this content. which explains the process of how to do it. It explains everything from downgrading to Jailbreaking and so on... follow the steps below.
Follow these steps here:
Step 1: Download "MinVerCheck"
You must login or register to view this content.
Step 2: Extract the folder using whatever programme you use to extract files such as Winrar...
Step 3: Create a folder called... "PS3", within the "PS3" folder create a sub-folder called "UPDATE"
Step 4: Place the PS3UPDAT.PUP in the update folder...
Step 5: Go to Settings > System Update > Upload Via Storage Media > Click "Ok" once it finished scanning the .PUP and it will tell you the minimum firmware that can be installed on your PS3
Remember it must be less than or equal to 3.55 in order to downgrade it.
You must login or register to view this content.