In a nutshell, you need to install the DFU tools to upload the bootloader via usb. After that you can update easily the firmware using the Mission planner. Don’t forget to set the jumper to boot from flash.
More details about the datasheet can be found here. The connectors pinout description are the same as the pixracer, but take caution with the GND on connectors since some are inverted. If you know the ground you automatically know the correct order of the pins. Use this for your reference.