Upgrading the firmware
Please note that you must have a Developer Key to follow these instructions. (On a laptop with security enabled, you must have a developer key to get access to the ok prompt. From the ok prompt, you have complete access to all of the hardware's capabilities, so allowing unrestricted access to the ok prompt completely disables the OLPC security features.)
How you update the firmware depends on what method you can use and what board type you have.
 Finding your current firmware version
The version of the firmware is displayed by Open Firmware when the laptop boots and prior to loading the kernel. The version number is a series of 5 digits after the text
An example would be 'Q2B74'. The last 3 digits of this string (B74) are the most important. The 'B' stands for the 2nd major revision and originally indicated the target board for the firmware ie. BTest. The 4th major revision 'D' is being used for mass production laptops. We try hard to keep backwards compatibility so later series of firmware (with a few exceptions) run on earlier boards.
The 2 digits are the revision number of that firmware. Higher numbers equal more recent firmware versions. On B4 machines, the firmware version is not displayed on startup, but can be found using the command:
dmesg | more
on the terminal (Ctrl-Alt-F1 and login as root). This will show a line like:
[ 10.210194] OLPC board with OpenFirmware: CL1 Q2C18 Q2C