Electricians please help. The house Breaker keep knocking back when I turn on the light?

Off hand I would have to say that something got shorted during the mounting process. Is it possible you ran a screw into the wiring that cleared when you removed the can from the ceiling? Try connecting the light and install the led kit while it is hanging to make sure there isn't a problem with the kit. It would not be the first "brand new in the box" part to be faulty. Being as it only trips the breaker when you turn the light on the problem is somewhere between the switch and the LED kit. If the light works when it is hanging, the wiring must have shorted when reinstalling the can. If this is the case, try and locate the damaged wiring. If it trips with the LED kit installed, you are either not connecting it correctly or it is faulty.

Most likely the hot wire (black) is shorting when you close the box. Make sure your connections are taped up. When you close the box up make sure the wires are seating into the box and not getting crimped between the box and the fixture.