The Mu editor releases are available on the Mu download page. If you want to test an updated or custom version of MicroPython with the latest micro:bit, you can do so in the following way:

  1. Flash the micro:bit with the version of MicroPython you want to test.

  2. Click the REPL to communicate with the board directly via serial.

  3. To download a python file to the microbit, Click on Save and then click on the Files button.

  4. Copy from the Files on your computer to the Files on your micro:bit