High Scores not working.
You need to sign in into GameCenter to use the high scores and achievements. Please use the GameCenter app to sign in using your Apple ID.
Downloading stuck from iTunes App Store.
Restart your device, Turn on and off wi-fi/cellular then try downloading again.
Try downloading the app via iTunes on your computer then sync with your device.
You will not be charged for downloading again as you've purchased it once.
How to uninstall an App from my iPhone or iPod?
To uninstall an app you simply need to touch the icon and hold it for several seconds. All of your apps will start to shake a little and an "X" will appear above them. Tap this "X" to uninstall the program. You can tap your home button to return your programs to normal function.
How to close iOS Apps running in the background?
Press the Home button two times quickly to access the multi-task bar on the iPhone/iPad.
Four running apps are shown on the bar, if you scroll to the right, you will see all apps that are currently open.
Press down on one of the apps until a red circle with a minus sign appears on each item.
Tap the minus sign next to each application you want to close.
Press the Home button to return to the main screen.