The fastest you can drop in is an 840QM, which is only a little upgrade.
I'm not sure about the GPU - you could whip off the bottom serviceable area and try to look to see if you can see a card with heatpipes coming off it. There's no way you could drop in a 580M though - not to replace a 335M. The TDP difference is huge. You maybe get away with.. a 540M/550M/640M/650M range, but I don't know where you'd find these and even if they'd fit.