To update your iPad use the following steps:
1. Tap on Settings
2. Tap on General
3. Tap on Software Update
Depending on how old the operating system is, this can take several minutes. The iPad will restart itself when finished. If your battery is less than 75%, plug in while doing this process.
If your iPad fails to update because there's not enough space available:
Delete apps, photos, and videos
Meraki Self Service Portal (delete apps)
Backing Up iPad Photos Using Google Photos App
iPad Troubleshooting