Vadamo :
I read that laptop cpus are upgradable, depends on which laptop you have. I upgraded my compaq presario cq60, but the PCG-531 have no manual,specs, NOTHING!
If it's got nothing on it, then I would, erm... be suspicious of if it had been built so that it could be upgraded.
However, you could always open it up and check out the motherboard and processor and see if it looks possible.