The new Megatronics 3.2 has a special header for connecting the Nextion displays. This allows you to easily add a LCD with touch screen function, without impacting the performance of the 3D printer, as the Nextion takes little CPU power away from 3D printing.
The Nextion LCD comes with a cable that connects on one side into the LCD and at the other side has four strands:
These strands match the order of pins of the Nextion header (NXT, near the SD card) on the Megatronics board starting from pin 1 (marked with a little 1). So connect the the wires as shown in the picture on the left.
After connecting the wire the electronic setup is done. Now proceed with uploading images to the LCD.