I don't have such instructions but am encountering folk that install non-Carrier or non-Maker OSes. My thought is that lesson is going to be repeated.
Ask Sony how to go back. If you got this OS from some forum, they usually know how to go back.
I have bought SONY XPERIA U just a month back & few days back only i have upgraded to ICS 4.0, after upgrading i don't feel it's of any use,it is verry verry slow & some time i am not getting message tone & mail alert tone etc,, there are lot more issues, i want to downgrade ICS to Gingerbread 2.3.7.
need your help on this