I guess it's a little complicated...but any tech savy person could do it. There are detailed instructions on the process, kinda hard to mess up as long as you follow them and take note of my changes. As for losing your data, I just copied my person...
I manually upgraded my fido Nexus S to ice cream sandwich using the official full 160MB upgrade (for T-Mobile) supplied by google. First I had to install the pdanet usb drivers on my win7 pc because the ones supplied by google didn't recognise my ph...