K-6, that an old one.
You'll need a decent motherboard that will allow you to adjust the CPU multiplier, the CPU bus speed and the CPU voltage. A lot will depend on the quality and speed of your RAM as well. It would also be a good idea to look through your motherboard's manual to know where to look for the following adjustments as well as the CMOS reset jumper. If your board doesn't have a CMOS reset jumper, you can reset it by removing the CMOS battery for a few minutes.
IIRC, correctly the K-6 ran at 2.2Volts.
Lower your multiplier to 4.5 or 4 and start raising your bus in small increments. Monitor your temps, and keep checking for stability. Pretty soon you'll reach the limits of your RAM. This will give you an idea of how far you can take the CPU bus up to. Once you've found the highest bus speed that's stable, try raising the multiplier back to 5. Monitor temps and check for stability. If the system becomes unstable, raise the voltage to 2.3V and see if it helps. If you cannot adjust the voltage at all, you'll have to either lower the bus, or multiplier. I would start with the bus first. Small increments, monitor the heat, check for stability and so on.
It going to be trial and error to find the best combination of voltage/multiplier/bus speed to find an optimum overclock.
Good luck.