@dlalvarez I also purchased just the modules.
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.