I went ofw 3-41 > ofw 3.50 > cfw KMEAW 3.55 with my ps3 slim
. if you dont have a dongle or anything to get in to recovery then that is the way to go in my opinion.
If you do it the way illusionsofgrander sugests you will find you need a dongle or something (a psp or compatible phone maybe) to get it in to recovery mode and do ofw 3.55 to cfw 3.55.
All you need is a usb memory stick