Advertising is how we support the development and delivery of the free version of FreeCell.
If you prefer to play our game without ads, we also offer a paid version of FreeCell for $4.99 no advertising. You can download the paid version FreeCell here - http://itunes.apple.com/us/app/freecell/id284862767?mt=8
If you do purchase it, a separate install of FreeCell will be the paid version. The free version will not be overwritten or removed as it is a separate application.
Just note that if you do purchase it for $4.99, that the statistics are not transferred over as Apple treats every application independently, so you will start fresh.