Hi and welcome to LQ!
Details, details, details. that's what we need to help you.
1. What exact version of ubuntu were you using when your wifi was working well? (there is no version 11 of ubuntu).
2. What driver were you using for the wifi before the update?
3. What version of Ubuntu did you update to?
Your problem is discussed in much detail on the ubuntu forum. You might want to learn to search for these things yourself.
I have a look a this thread: http://ubuntuforums.org/showthread.php?t=1580036
. It contains some detailed instructions.