If your PSP is a TA-82 model then follow this guide:
http://forums.maxconsole.net/showthr...highlight=2.71
But only follow it as far as downgrading back to the 1.5 firmware, as you will then want to upgrade to the custom firmware 3.03 OE-C, which I can explain next.
Or if you PSP is not a TA-82 model then you can follow this guide:
http://www.psphome.com/forum/psp-tut...sp-1-50-a.html
When doing either of these methods make sure you first fully charge up your PSP to 100% and then during the process of downgrading the PSP make sure the mains power supply is also connected to the PSP at all times. If you don't do this it could go wrong and kill/brick your PSP.
Also before you start I recommend you format the memory stick in your PSP, and then once downgraded to firmware 1.5 you format the memory stick again before doing the 3.03 OE-C upgrade.
OK, if you have done that and now have a PSP with firmware 1.5 you are ready to upgrade to the custom Dark_AleX firmware 3.03 OE-C. First before you do anything format the memory stick just to make sure it is clear and fully formatted to work correctly with the current firmware in your PSP.