Non destructive Bebop "firmware update"

The wiki specifies that a “new firmware” has to be installed on the Bebop, for ardupilot.

Where do I find information about it? specifically:

what [color=#FF0000]version [/color]is that kernel?

where is the linux [color=#FF0000]source [/color]+ kernel config file?

which [color=#FF0000]compiler [/color]to use?

will that “firmware upgrade” clear all [color=#FF0000]filesystems [/color]on the Bebop?
(or just replace the kernel, leaving the filesystem unmodified)

Can I upgrade the firmware and use Bebop as before?

Can I revert back to Bebop firmware? how?