Once you download something, Apple remembers it for life. It will show up in the Purchased tab of the various iStores. That does not mean it is on your iPad. It just means that if you ever change your mind, you can download it again.
That often comes in handy; even with apps you decided you did not want after all. Sometimes they get better, a lot better.
If you are talking about not being able to delete an app from the iPad, you can delete anything that did not come pre-installed as part of iOS.
Tap and hold on any app. When they all start to jiggle, tap the (x) in the top left corner of the icon to delete the app. While in this mode you can also drag apps onto of each other or existing folders to organize them.