To sum it up, if you're upgrading from 5.4:
1. Go to the B&M site download section and get the B&M Configurator
2. Unpack the configurator on a USB stick and follow the instructions to run it (on your car). This will generate a config file on your USB stick
3. Get back to the B&M website and upload the config file (from the step 2), to reveal your B&M firmware update download options
4. Download the 5.5 update, unpack it on a USB stick and follow the instructions
5. Repeat steps 3-4 for the 5.6 update
When updating (in the car), don't get impatient. The update takes a while, with little indication that it's still going. Mine took about 10 minutes each (5.5, then 5.6), during which I thought it hanged.