Remove the four screws from the bottom, then take off the back cover. This is also how you access the battery. You need to take off one of the circuit boards to access the chip. It's the smaller board where the micro SD card slot is housed. There are two hexagonal posts you have to remove. In the photo below I've already removed the lower one. The other one is next to the black O. I didn't have the proper tool to remove it, but needle nosed pliers were good enough.
Once you've got the screws out you jiggle the board until it comes off. Turn it over and you can see the lovely litttle components and chips.
My 2.4 firmware chip arrived all safey packed on a bit of sponge. You prise off the old one and put in the new one. See the video below for further information on doing this. The only tricky part is bending the legs inward to make them fit in the socket.
After you have the chip in place, carefully reassemble the two boards. You have to line up the two connecting sockets on the board you removed, with the pins on the board still attached to the case. It's best to do them one side at a time. They are different sizes, so it's pretty clear which way it should go.
Then put the hexagonal screw posts back in, reassemble to case and outer screws and you should be done.
WATCH THIS VIDEO TO SEE THE SAME CHIP BEING REPLACED FROM A SIMILAR INSTRUMENT.
Thanks to the guys at Bastl for pointing me in the right direction. This is a bit of a DIY product, so I didn't mind the fact that there were no instructions, especially because I got a pretty clear answer when I posted to their facebook page asking for help.
Here is a track I made with the old 2.0 firmware.
And here I am fatrarsing around after installing the 2.4 firmware, not really knowing what I'm doing..
Now hear this: your electronic dream device is not mass-produced in China by a mega-coproration. It's made in a garage by a teenage genius. Technology for the masses, BY the masses.
PEACE AND LOVE