You'll need either linux or OSX and then make sure to download the flasher-3.0 utility for whichever operating system you're using (there is none available for Windows). Then download the image from nokia. You can search the forums and google and you ought to be able to find it (the image file is called RX-44_DIABLO_5.2008.43-7_PR_COMBINED_MR0_ARM.bin).

Once you have the flasher and current Diablo image downloaded. you'll need to run the command: 'chmod +x flasher-3.0' to be able to use the flasher. Then run the command: sudo ./flasher-3.0 -f -F RX-44_DIABLO_5.2008.43-7_PR_COMBINED_MR0_ARM.bin --flash-only=kernel