Originally Posted by Mitrigol

okay, you can find better info there: http://wiki.maemo.org/Updating_the_firmware

You have to shut down your phone

open keyboard, press u and connect it to you computer via USB.let drivers install.

Now fire up your terminal and type the first command:

flasher-3.5.exe -F youremmcfilename.bin -f

wait until finish, Do not boot your phone!!!

Disconnect phone from USB and remove battery fro a minute.
Put the battery back, reconnect the phone while holding U button

in your terminal, type the second command:

flasher-3.5.exe -F yourrootfsfilename.bin -f -R

This should do the trick.