@ToorboPSP:
please dont hijack other user's threads. that being said, i can answer your question. since you have 5.00 m33-6, that is the latest version of the full m33 cfws. if you wanted to update, you would have to go to 5.50 gen-d/d2 like you said, but you would have to update through the usb.
5.03 m33-6 (also known as cfwenabler 3.50) is the latest version of the
partial custom firmwares by xenogears and becaus25. you probably wouldnt want to install a partial cfw when you already have a full cfw installed.
if you want to update to 5.50 gen-d/d2, just check these links:
Custom Firmware 5.50 GEN-D2 Released | Download CFW 5.50 GEN-D2, PSP Hacks - PSP Slim Hacks
Custom Firmware 5.50 GEN-D2 Released | Download CFW 5.50 GEN-D2, PSP Hacks - PSP Slim Hacks
i hope this helps clear things up