cannot be downgraded through simple software menus because Sony's system prevents installing older versions. Scenario A: Your PS3 has Custom Firmware (CFW)
If your console is unmodified and running official 4.89 software, you cannot directly downgrade using a USB stick. You must use tools like the PS3 Toolset to jailbreak your console first. how to downgrade ps3 firmware 4.89 to 4.88