Pot is short for potentiometer. Its just a variable resistor:
The volume control on your stereo is a "pot". So is the volume and tone control on your guitar.
Generally, 500k pots work best with humbuckers, and 250k work best with single-coils. So, you'ld only need to change it if you switched along those lines. And even then, its not absolutely necessary. Just a general guideline.
BTW the "k" means times 1000: 500k = 500,000 ohms.