Apple will not allow changing of iPhones, even if you pay out of warranty fee of $199 for 4S, or even more. If you have Warranty or AppleCare it will be covered, with replacement 4S. If you want iPhone 5, you will have to just buy one as usual.
Follow the instructions in the article from which your question was posted.
If the issue continues, Apple will replace with same model, color, and capacity.
Apple does not provide upgrades.
If you want an iPhone 5, buy one.