How to downgrade PSP OFW 6.30 to CFW 5.50 GEN-D3 for psp 3000?

I'm a noob with this stuff but as far as i know you can't do anything cfw with a 3000 or Go so i don't think you can downgrade, i have a phat and i'm trying to do the same thing as you.

At this point in time you cannot, and even if you could, for someone with 'next to nothing' knowledge on this subject. You could potentially brick your PSP and get your computer viruses from trying to download .ISO images (free psp games) in your case. Take my advice even if it is only for homebrew, custom themes, and plug ins, it is better to just play it with the OFW. I'm positive you will have to wait for another user exploit, and even a smaller chance on the kernel exploit. So no you can't downgrade then go straight to CFW, there is a process and if you're serious about wanting to learn how that process works, so you don't get 'no or smart aleck' anwsers, then I suggest going to PSP development related forums and learning there off of their tutorials.