Hello. It might be a stupid question but i searched the forums and didn't find what I needed, so, here I am asking the stupid question

I have a japanese PSP with 2.5 firmware. In order to downgrade with the new downdater i heard I should update to 2.6 First. But i couldn't find a japanese 2.6 firmware update anywhere. So, the question is: Do I have to update my japanese PSP with japanese firmware or can i just put the USA one. And second, do I really need to update at all...

Thanks to all that might answer.