Upgrade your iPhone or iPad to the new iOS
Before upgrading your iPhone or iPad, it is very important to make sure it is running well and that it is freshly backed up. You may think your device is running well, but it may have some problems that are not evident to you. A restart usually fixes this problems.
Hold the power button of your device (top right or upper right side) until you see “Slide to power off”. If you have an iPhone X or newer, hold the power button and volume down button at the same time.
After about 30 seconds, hold that same power button to turn your device back on. Fully unlock the device. You should see your home page.
Now, let’s backup your device (make of a copy of its apps, settings and your content - pictures, videos, emails, texts, etc.) to somewhere safe like iCloud. This is the most important part of updating so you can get back to where you are if something goes wrong. I recommend you use iCloud to do this. Your device will need to be on Wi-Fi for this to work:
Open the Settings app, click on your name then click iCloud.
Scroll down to iCloud Backup and tap it.
Make sure that iCloud Backup is switched on. If it is not, tap it to turn it on.
Below that, tap “Back Up Now.” Wait for the backup to complete.
Note: If you get a backup error it is often that there is not enough room on iCloud to backup. If that is the case, go to Settings > [your name] > iCloud > Manage Storage > Change Storage Plan. Buy the $0.99/month version of more iCloud Storage then go back to the steps above to try backing up again.
Finally, go to Settings > General > Software Update and follow the instructions to upgrade your iPhone or iPad.