We have the NLMC and it's not too difficult to replace the lamps. As Woody said it should have came with a tool the release the locking clip and then you can unscrew the lens. Even without the tool you can pry the locking tab back with a flat balde screwdriver.
A word of caution: When installing or replacing the lamp wear clean cotton gloves to handle the lamp(s). Even a very small amount of oils on the lamp will severely shorten the life of them.
I'm not at home so don't have the model # on our lights, but I'm pretty certain we have two of the 50s ... neither of which worked this year as the bulbs are bad
Our local pool store does not sell this model bulb, but the owner looked it up & her price will be $40 each (that's half what we paid for each light!) My husband found what appears to be the exact same bulb (looks the same visually, has the same wattage/model #) at Wal-Mart in their standard light bulb section. Of course, that bulb does not say "pool safe" and we're afraid to use it without some advice.
What are other Nightlighter owners using to replace bulbs?