Board Thread:Questions and Answers/@comment-68.175.106.42-20151212165952/@comment-69.28.44.76-20151214025411

You don't,  As of last year they discontinued the product and only allow purchase of the Steam version (which I believe is superior, and its cheaper :D)

You can buy it on Steam for $10.

The original NinjaKiwi purchase page for BTD5 Deluxe no longer works.