go to this link and download the ITA firmware of your choice:
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once you download it open the RAR file. then plug your USB into your computer.
Make a folder in your USB called PS3 then in that folder make another one called UPDATE and put the PUP file in the UPDATE folder so it should look like this. USB>PS3>UPDATE>PS3UPDAT.PUP
Remember to rename the ITA update to PS3UPDAT or your ps3 wont find it.
once done remove your usb and plug it into the furthest right usb port and then go to update system then choose from storage device and bam done