so on Jan 2009, you will have 5 years of ownership? If not your free service has not expired yet. And why are you doing your own oil change at 28K miles (I saw your other post) when you can get it done free?
Back to the spark plugs, you have a long way to go before you change the plug so I would not worry about that. But if you have all the tools, it should not be an issue to do it yourself. GL.