"Base SDK Missing", how do i set the minimum required OS to ex 4.0 in sdk 4.2?

What I want to do is to set the minimum requi开发者_如何学Cred OS to 4.0 instead of 4.2<... Is there anyway to set the base sdk to 4.0?

Set the “iOS Deployment Target” value in build settings to control the minimum required OS.