How can I abort a stalled in-progress app update?
This is addressed several times on the Apple Forums.  It is a common problem.  I will list a few of the answers that have worked for others. Before starting, do the obligatory iPad reboot.

1) From the iPad desktop click the stalled app. It will either restart the update process or report the "update failed". If it fails you will then be able to restart the update from within iPads App updater.

2) If you have a desktop Mac, from iTunes go to menu Store > Check for Available Downloads. This should download the updated App to your iTunes. Then re-sync with your iPad.

3) Delete the app from your iPad then reinstall.

I found that option 1 worked flawlessly for me.