See https://weekcalendar.zendesk.com/hc/en-us/articles/205562612 if update does not start at all.
Sometimes iOS applications get stuck waiting or loading when installing. These apps might be frozen with a blank icon and no way to remove them for days. Holding down on the home screen to delete the stuck app won't even show the black circle with an "x" that appears on other icons. Here are instructions on how to delete these waiting applications.
If you have a computer at hand you can skip steps 1 & 2, step 3 is fastest method.
- Reboot your device normally by holding down the sleep button on the top of the iPhone. A red slider will appear at the top of the screen that says "slide to power off." Slide this arrow to the right and the iPhone will power down in a few seconds. After the device is completely off, the sleep/wake button can be pressed to turn on the device.
- If the apps are still stuck on the home screen, try logging out of the App Store temporarily.
Navigate to Settings -> Store -> Apple ID -> Sign Out.
Now open the App Store and Navigate to the Featured section.
Scroll to the bottom of the page and touch the Sign In -> Use Existing Apple ID. Log in and the stuck apps should reset.
- Still have strange icons on the screen or frozen downloading apps?
Connect your iOS device to the computer and open iTunes.
Navigate to the app store.
Install the apps you are having a problem with on the computer then sync your iOS device.
iPhone6 users: use the lightning cable
- Disable sync over Wi-Fi.
- If it's already checked off, set it to on and hit apply. Then turn it off again and hit apply again.
- Turn the device into Airplane Mode and turn Wi-Fi off. This will make sure it definitely uses the cable and doesn't get confused and hang up.
- Now restart iTunes and force quit if you have to.
- Now start syncing by plugging in your lightning cable
Move the Icon with the stuck installation to another page and try to install again
Tapping on icon while it's downloading actually pauses the install. You can easily tell if you've accidentally paused an install if it has a pause icon over it with the word paused underneath it. However, even if the install doesn't seem to be paused, tapping on it can sometimes trigger a frozen install to pick up where it left off again.
Download another app
For some reason, downloading another app from the App Store can make stalled apps start to download again. So simply head into the App Store, find a free app to download. Any old app will do and it can even be something you've previously purchased. Wait a few seconds and see if that kickstarts the stuck app.
Sign out of iTunes completely and reboot
If all else fails, signing out of iTunes on your device should terminate any downloads you currently have in progress.
To be sure, after you've signed out, simply reboot your device before signing back in.
- Launch the Settings app on your device.
- Tap on iTunes & App Store (you'll need to scroll down a ways)
- Tap on your current Apple ID at the top.
- Tap on Sign Out in the popup menu that appears.
- Sign in again