I got help from a member of QJ.NET, GPSosa, so I decided to left thanks post.
I PMed GPSosa about a couple of days ago and asked him that I have PSP with 3.52 fw, so if he can help me. He said, no problem, and gave me his phone number.
I called him this afternoon, he even came to my place to do downgrading and installing cfw. It was really amazing to see how fast the process had done. He backed up my flash0 and some instruction on the theme changing.
Again, I really appreciate your assistance, GPSosa as well as devs of pandora battery.
However, the story didn't finish here.
After GPSosa left, I was little too excited and the fact that I made back up of flash0, the long story make short, I messed up. Only the backlight is on and nothing happens when I turn my PSP on. Even the recovery menu doesn't show up, which means I couldn't do anything about it now. I guess this is so called bricked :Argh:
Oh well, I guess I need to call GPSosa again for help.