How can I install official Android 2.2 Froyo in Samsung Galaxy S which runs Android 2.1 Eclair? How can I install official Android 2.2 Froyo in Samsung Galaxy S which runs Android 2.1 Eclair?
Depends on your model.  For most of the international versions such as the GT-i9000, you can get it over the air (a notification pops up, ir you can go to Settings -> Software update) or through Kies (I recommend getting Kies Mini from Samsung.com).  Froyo has not been officially released for some models including the US ones, however.  I recommend a custom ROM such as Nero v5 for the T-Mobile Vibrant.  The easiest way to find one is to go to XDA and look and the subforum for your device.  Note you probably need root and ROM Manager (in the Market) to load a ROM.