Here are some things that you can try.
Close the App Store. Press the Home button two times quickly. You'll see small previews of your recently used apps. Swipe left to find the app you want to close. Swipe up on the app's preview to close it. Then restart the iPad and try again.
Try a forced restart. No data is affected by this. To force restart your device, press and hold both the Sleep/Wake and Home buttons for at least ten seconds, until you see the Apple logo. When the device is fully up and running, try to install an app.
Try tapping on the circle to stop the download, then tap Update again. Try it a few times. Sometimes that will resume the downloads.
Go to Settings>Airplane Mode>On. That will disconnect you from your WiFi connection. Give it about 30 seconds and then Turn Airplane mode off. Try downloading again.
Power cycle your router. Unplug it from power for about 30 seconds, then plug it in again. You can also restart the iPad while the router starts up. Then try downloading again.