Can someone tell me how to downgrade a psp version 4.05 to 2.0 or 1.0?

Question

Or give me a website thats displays how thank you1 :)

Answer 1

copied from the attached link:

Downgrade PSP v2.00 firmware to v1.50

It has finally come! A PSP 2.00 downgrader by MPH. So many PSP users who wished to run homebrew on their device were stuck with newer firmware such as 1.52 or 2.00. This made running of homebrew code impossible. I believe that everyone should have the right to run their own code and we all shouldn't be limited to "authorized code" after spending money on the hardware. This is NOT a guide to show you how to pirate games for PSP. This is intended to show users of 2.00 PSPs how to downgrade to run legal homebrew, that's all!

Introduction and Requirements

NOTE: WHILE THIS METHOD HAS BEEN TESTED AND SHOWN TO WORK FOR MANY PSP USERS ALREADY, THERE IS NO GUARANTEE THAT YOU WONT s***w UP YOUR PSP BY TRYING TO DOWNGRADE. THERE IS ALSO NO WAY OF TELLING IF THERE WILL BE ANY FUTURE PROBLEM DUE TO DOWNGRADE. IF YOU BREAK YOUR PSP, TOUGH! IT'S NOT MY FAULT AND IT CERTAINLY ISN'T THE FAULT OF MPH EITHER! YOU ARE THE ONE THAT WILL BE DOING THIS, NOBODY ELSE, SO IF YOU DO IT WRONG, OR ANYTHING BAD HAPPENS, IT'S YOUR FAULT!

But anyway, out of the legal stuff and back on track ;-) You need your PSP obviously, a Memory Stick (32MB will be fine), USB connection (or some other method of transferring files to Memory Stick - but be warned, I used a USB connection for my test, I didn't test with any other method of editing Memory Stick), the MPH Downgrader and most importantly, the 1.50 Update Eboot file.

We don't host any of those files yet, but I'm sure you will have no problem getting the files from other sites like PSPUpdates (excellent source for PSP news if you haven't noticed that already!).