Advertising is how we support the development and delivery of the free version of Spider.
If you prefer to play our game without ads, we also offer a paid version of Spider Solitaire with no advertising. You can download the paid version Spider Solitaire here - http://itunes.apple.com/us/app/spider-solitaire-by-mobilityware/id391855805?mt=8
If you do purchase it, a separate install of paid Spider will be installed. The free version will not be overwritten or removed as it is a separate application.
Just note that if you do purchase it, the statistics are not transferred over as Apple treats every application independently, so you will start fresh.