How to Use an External ST-Link/V2 with the STM32F4 Discovery Board

You'll need to isolate the microcontroller from the st-link portion of the board. To do this just remove the jumpers on the CN3 pins.

Then, to use your external st-link, make the following connections to the microconroller pin headers:

• SWDIO -> PA13
• SWCLK -> PA14
• GND -> GND

• VAPP -> 3V/VDD

• Do not connect the USB cable

Program it in SW mode.

Not sure why you'd want to do this, unless you wanted to use JTAG to program it instead. If that's the case let me know and I'll update the answer.