You'll need to check whether you need a downgrade or ODEs
1. Download
You must login or register to view this content.
2. Make a folder on your USB stick called PS3, inside this folder make another folder called UPDATE (both in CAPS)
3. Put the PS3UPDAT.PUP from MinVerCheck into the UPDATE folder
4. Turn on the PS3, insert the USB stick and navigate to Settings -> System Update -> Storage Media
5. When attempting to install the update, it will notify you of your minimum version. If it is 3.55 or below, you are able to downgrade your PS3...
If the minimum version is not 3.55 or lower you will need to have a ODE...