What I did was I used these files and the guide that is down lower if you scroll down.
http://www.pspmod.com/forums/downloa...?do=file&id=22 It installed cfw 3.71 m33 2. After that I just went to 3.71 m33 4 from downloading updates off of dark alex's site. I then did the 3.80 update off of the dark alex site. From 3.80 you can run all of the updates over network update on the psp. There is prolly a easier way to get to 3.90 now...but when I hacked my psp like 2 months ago this was one of the more up to dates on how to do it since 3.80 wasnt even out yet.