newbie question about android upgrade

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http://androidforums.com – Hi guys till a week ago i had an iphone (run over it with the car) and i was sure that android phones sux, i was wrong iv seen that i can buy a phone a Chinese phone that is more powerful than iphone and less expensive and even look better. But the phone that i want come with android 2.3 and i really have no idea what is going on with android. is it possible to upgrade manually from 2.3 to 4.0 or any other version ? what is the difference between the versions ? can any phone support higher version then it have ? does android version support specific phones or its like ios that work on 3-4- (General)