Bangle.js v2: how to update Firmware?

Thus, my current tips are:

• if nrfTools give you the message
  xxx bytes were sent while 0 bytes were reported as received
  just retry - even if you have to retry approx. 100 times! (it still only takes a few minutes
  
• after completion, connect the Espruino Web IDE with your Bangle.js and check, that the terminal displays the correct (i.e. new) firmware version!