If you want to permanently delete them from your account (as if you never had purchased them) do the following: Open iTunes on your Computer you synced the iPad with (or any other computer authorized with the Apple ID you bought the apps with). Got to the Option "Apps" (left hand side, pretty much at the top of the list), then find the app(s) you want to delete, right-click on them and choose delete. Hope this helps. The next time you sync your other devices with your iTunes Library (if you have an other device e.g. iPad) the apps will be permanently deleted from them, too. Hope this helps.
If you want to just delete them from your device (say iPad/iPhone): Sync your devices with your iTunes LIbrary, select them in the left hand side options bar (under devices...you'll see it), then you will be presented with a summary page of that device. Select Apps (from the options menu at the top of the page) and unselect the App(s) you want to delete from your device. Sync your device again, and you're done.
Hope this helps.