try to back up your save data just to make sure,
is your PSP hackable?
are you trying to downgrade or upgrade just to clarify?
there is a known 6.20 downgrader for unhackable psp somewhere though once you are successful with the downgrading, you'll encounter a BSOD which was said to be normal....
-------------how to uninstall CFW-------
you should have the installers you used to install PRO-C on your 6.39.... first, if you're on permanent patch, uninstall first the permapatch , once done, uninstall the CFW it self via UPDATE... run it and you should see UNINSTALL there, probably triangle or L..... then you are now on 6.39 OFW...
-------------------downgrading-----
if your psp is hackable, you probably can use pandora and magic MS to downgrade your psp,
IF NOT HACKABLE... you must use the 6.20 downgrader..
------------updating to higher OFW-----
if your psp is clear on CFW... just run a official installer of OFW of your choice but you probably should aim for 6.60 ( IF YOUR PSP IS HACKABLE ) not just because it is the last OFW update, but because you can your ME to if you like ME than PRO.....
IF NOT HACKABLE... try to downgrade to 6.20 since it has permanent patch that acts as a FULL CFW...
though i think 6.39 has permanent CFW of PRO but i am not sure..... try to ask others more if your have doubts