Default [Q] upgrade xda iis to the latest windows

I own an O2 xda iis currently having windows 5.0 installed. And i have gone through many forums and websites to get my device upgraded to latest rom and windows version available. I am confused regarding the selection of the rom, windows and the exact procedure. Anyone who could help me exactly with my model xda iis is greatly anticipated. I already have the latest WMDC and usb cradle.Please help.