How to change keyboard settings from American to British Settings?

I reformatted my computer recently because of a computer virus, all the settings where restored except for the keyboard settings. Some of the keys when pressed will give another character and i found that it follows the American type of keyboard settings. How to restore it back to British settings?|||if you already have your OS installed.... you must re-install it. and when you do, at the progression of the set-up, there%26#039;s an option there on to what type of keyboard setting you want to use.