How To Upgrade My PSP System Software Version 4.01 M33-2 To Version 5.50?

I don't recommend that you do. You should simply upgrade to CFW v5.00 M-33. Unless you have had problems with the M-33 series of CFWs, you should stay with them. Generally the Dark Alex CFWs are extremely stable, and will serve you well.

Hope that helps, and you have a great day!
Asuka Jr.