Thanks to the people at the Panasonic forum at www.dpreview.com, here are the instructions and firmware upgrade for your FZ1. No guarantees, at your own risk etc. - I haven't tried it myself yet, but others say it's fine.
1) Make sure you have a fully charged battery inside FZ1 (VERY IMPORTANT) plus AC adaptor just in case
2) Download firmware.bin (811k) at http://www.2000wuben.com/firmware.bin or here.
3) Copy the file to SD card - the SD card should also have 2 empty folders MISC and DCIM
4) With the camera OFF, insert the SD card, turn the switch to playback (or review mode)
5) Turn ON the camera and you should see ENGLISH upgrading information. If not, you should turn OFF the camera.
6) Choose FIRM/EEprom (furthest on the left), push SET (downward arrow) on the back of the camera, then the LCD will go blue.
7) Wait for about 2 minutes until the on/off light stops flashing.
8) Turn OFF the camera, remove the SD card.
9) Put another SD card into the FZ1, and you have an FZ2!