Upgrade the firmware
Upgrading the firmware is a pretty straight forward process, and it does not require any special tools or procedures apart from the official way, regardless of the Media Nav generation. Tutorial: Upgrade the firmware.
Downgrade the firmware (MN1 & MN2)
Sometimes, downgrading the firmware may be necessary, for incompatibility issues or for using software that was designed for an older firmware version. Tutorial: Downgrade the firmware (MN1 & MN2).