@Astonishing1: Do you have sufficient internal storage space available on your Galaxy S8+, as this can affect your ability to install apps, and perform app and system updates. To check, please head to Settings > Device care > Storage.
If you're having trouble updating your device, as well as backing up your personal data, then I recommend trying Smart Switch on your home computer. To begin with, please follow the link below, and click on 'How Do I Get Smart Switch On My PC or Mac' to download the relevant version
https://www.samsung.com/uk/support/mobile-devices/how-do-i-backup-my-smartphone-to-my-pc-or-mac/
Once installed, open Smart Switch, connect your S8+ using the USB cable that came packaged with the device, and look for an update prompt on the landing page, next to your device details. You can also click on the Backup tab and back up your personal data from here.
