There are two ways to do this:
1. Without opening the case, make a 2x3 block male pin to 1x6 wires and insert the wires into the breadboard's MISO, MOSI,SCK,RESET,+5 and GND pins. MISO, MOSI and SCK are next to each other for both micro-controllers.
2. Open the back cover, you can access the standard 2x3 ICSP pins for the ATmega16U2 and ATmega328P.