Your question has two possible answers based on what you meant.
1) If you mean how do you delete the app that you tap to run; Hold your finger down on the app until it wiggles and then press the red X for it in the right top corner.
2) If you mean how do you delete an app inside the list of apps you have purchased; You can not delete them, you can only hide them. Bring up the list of purchased apps, find the one you want, swipe it from right to left and select hide.