Download the rom of your choice from the above section
Download SuperRUU from here:
http://www.megaupload.com/?d=05KHW5A5
Set the phone in flash mode: turn on the phone while keeping the LEFT softkey pressed and connect it to the PC using the USB cable
Start SuperSUU, leave OS selected (DON'T CLICK ON IPL OR OSCP OR YOU'LL BRICK YOUR PHONE!), select the DIP file of the ROM to flash click on the "Update Target" button of the SuperRUU and wait for the process to finish.