The difference between the two kits is simply color temperature. One is 2700K (similar to an incandescent light) and the other is only a little whiter at 3000K (similar to a halogen light).
If we still have one or both options, you can find them here. Their price at the time of this writing is $12.95. They're moving quickly, so we encourage you to act now if they meet your needs!
As we've written about before, LED retrofit or downlight kits are used to replace traditional bulbs with a flush look that eliminates any evidence of the recessed lighting can. You can see in the image here that the connector is screwed into the socket like any standard light bulb. The wire arms are then folded upwards on their springs as the fixture is slid into place. There may be a small bracket in the recessed can that holds the arms, and their pressure helps to hold the downlight in place, providing you with a beautiful look to your ceiling.