How to remove a stripped screw from an iPhone 4?

Since APPLE is so kind as to tell me "You broke your iPhone's home button, you can replace the phone for $200 I decided I'll just open it up and replace it myself!" I just recently went to replace my iPhone 4 screen/home button and find a stripped screw that's connected the battery to the phone. How would I remove such a small stripped screw?

I heard using a Screw Extractor, but what size would I need to do this?