Some iOS 9 users report that they find problem on their apps because those apps won’t install or update. Sometimes, the updated app is already downloaded and it’s already on installing process. It displayed “Installing” on the screen but the installing process is not completed or failed in several seconds.
You can try to overcome this problem by several steps after you ensure that you have enough space left on your device by taping Settings, then tap General, and choose Usage, then see Manage Storage.
To fix your app that won’t install or update, you can try these steps: please open up the App Store and go to Updates then choose the problematic apps to fix them. Tap on the app icon right at the top left, and when it shown on your screen, please tap on the app icon to start the installing process.
You can try other way by opening iTunes on a computer or laptop then select the apps won’t update in your phone and please update them so that you can sync those updated versions to your phone after you plug your device in.
If those options are not working, you can try another option by deleting and reinstalling your apps. Please tap the Settings, then tap General, and choose Usage, then see Show All Apps and you can delete then download again and reinstall the apps according to your preference.
You also can try to reset your device by holding down together the Sleep/Wake and Home buttons for approximately 10 seconds. Or try to solve it by signing out via Settings, then choose iTunes & App Store, then choose Apple ID and turn off your device and turn it on again, then please Sign in again by taping Settings, then choose iTunes & App Store, and Sign in.
If those are not working, you can try to use reset factory option as your last choice. Please ensure that you already back up your data before this action.