How do I set the embedded ST-LINK V2 on a STM32F4-Discovery board (MB997C) to direct firmware update mode, so I can update the firmware?

[jr-edv]

STM32 ST-LINK (ST-LINK>>Firmware Update) complains about ST-Link not being in DFU (direct firmware update) mode.

[jr-edv]

As a connecting cable I used a cable by delock, which claimed to be a "multi flash reader" (device manager shows: USB\VID_058F&PID_6366). It somehow got in the way, although it made the discovery show up as a ST-LINK V2 and connected correctly. After using a regular A to mini-B, everything works fine, update including.