You will find the f/w files you need at the very bottom of this web page, all devices are in a single zip file:
A bit higher on the page you will find the CodeLoader PC software if you do not have it already.
If you also need the CodeLoader cable, it is available here:
A tutorial video for how to update a W-DIMm3 is here:
You can explore the rest of rc4.info to find even more helpful information!