I have lumines but i don't know if that downgrader-thing works for firmware 3.51+...

please help...

Hi MetalFacedMonster, and welcome to Console-Spot.

As you suspected, the Lumines downgrader only works for up to 3.50 firmware.
To downgrade anything above that, you will need to get hold of a Pandora's Battery and Magic Memory Stick.

You need the pandora's battery files, a memory stick that is 512mb or higher, but no higher than 1gb (Correct me if i am wrong) and a battery. Transfer the Files into the memory, run it and then the battery into the pandora's battery and it also changes the memory into the programs that runs with the battery(the battery and memory can no longer be used regularly). Then use the Pandora's Battery and it should change the version.

You can only make a Pandora's Battery using software if you already have custom firmware.
Otherwise you will need to either buy a pre-converted Pandora's Battery, buy a Datel TOOL battery, or convert the battery by opening it up and removing a certain pin.

in what terms do you mean that hx sucks??? i haven't decided to update my psp to 3.7+ cfw and i'm still using 3.40 le v3...

I originally misread your question as the important information is in the title.
You could downgrade from 3.72-HX to 1.50 via Recovery Mode.
Then you can upgrade back to M33.

he is right ^^

you should use the pandora battery to downgrade.
here is a complete and easy guide