You do not need to downgrade. If you are stock 2.2 (not using a ROM) you
can follow the directions starting at #1-Download the update from
Google. If you’ve already applied the update OTA, and still have S-Off,
you can skip to #8.

If you have not accepted the OTA, and aren’t running a ROM, i.e. you’re
stock 2.2, then start with step #1.