Before programming, make sure you have the right hardware revision.
Here you can download already compiled .hex-files for transfer on your cat flap.
Read Flashing to see how to flash the new firmware on your cat flap.
Attention: Use the correct binary for your flap. If its unmodified use the "normal" version. If you have added a poti use the "Poti" version. Otherwise the MCU may be damaged!