the resistor in question is the one marked "R1", its right above the LED on the PCB,
google "LED resistor calculator," and you'll find tools where you can enter in the specs of your LED, with a 5V forward voltage, and figure out the resistor you'll need without having to think about math at all!
swap out the LED, pay attention to the polarity when you remove the one in there (if memory serves, ground is the lower hole), replace the resistor with the value you need for the LED you used, thats it!
when you pick out your LED, look at its datasheet, you'll find all the info on its operating parameters...
but, a quick start is on colors red, orange, and yellow use a 220ohm resistor, on blue, green, white use 150ohm (am i forgetting an obvious color?)