Have a look at your motherboard...it may say words like 'cpu speed=multiplier x bus clock speed'. Near that area you should find some jumpers with your motherboard currently set at 4.5. Slide that jumber over to 5.0 and bingo - you got yourself a 500.
Now I've seen this done with a K6-2-300 with ordinary results (the processor didn't fry but the programs did!), and personally I don't recommend it.