To update the firmware you'll need to power the module, so VCC and GND. And UART1_TX and UART1_RX to the RX and TX of your USB to serial converter (make sure this is 3.3v, not 5v. I use a 3.3v FTDI cable). Connect BOOT0 to VCC for programming, and GND for normal operation.
That's all it needs.
Looks like your connection to RAK Support Center was lost, please wait while we try to reconnect.