Sorry to disappoint): Skip this step if you already have Firmware 6.60 installed on your PSP.
3.52 m33 to 3.71 m33,then 3.71 m33 to 3.90 m33,3.90 m33 to 4.01 m33 then from there you upgrade to 5.00 m33.here's a link i hope could help you..... it give instructions on how to update ur fat psp to cfw 5.00 m33.i know it sounds like a lot of work but it's a safe way that i know coz that's basically what i did.(i update my psp to latest cfw whenever it comes out so it's basically step by step update) i have 2 is fat and one is slim and i did not have any for your psp problem,you might not have the minimum required cfw to upgrade to 3.90 m33 which is 3.71 m33 hence the step by step upgrade.i'm using 5.00 m33-6 and its a great cfw.
If, on the other hand, you want to follow the easy method (which for now I recommend), please keep reading.
Installing Pro CFW on your PSP1000 is simple, free, and is not much risky than installing a Firmware update on your device.
Sony quickly patched this hole with the release of firmware 1.51.
Ok so im having a couple of issues updating to either of 3.90 m33-3/6, 5.00m33 or gen 5.02, im trying to get bleach heat the soul 6 to work and i heard these frimwares support it.