Update to version 2.2 on my HTC Hero Android 1.5 phone

Currently I am using HTC Hero with Android 1.5 and as we know right now Android 2.2 (Froyo) has been released, so i am planning to upgrade from 1.5 to 2.2. Regarding updating, I have the following questions: 1. How do I update it? 2. Is there any selection options provided to update? For example I want to update my 1.5 to 2.1 instead of 2.2, 2.0 or anything else. 3. Are there any issues that have already occurred with Android 2.2? 4. What if I want to down-grade to lower version, is it possible? (i.e. rollback to older version)