Before updating your iPhone to the lastest version of it’s iOS always a good idea to backup, just in case the update fails to migrate your data. Follow these steps to use iCloud for your backup.
Go to Settings
Scroll to iCloud
Storage & Back up
Switch iCloud back up On
If you have have more data on your iPhone than the free 5GB limit you will be warned when you attempt to enable the backup. In this case choose step 2 below which will either say ‘Buy more space’ or ‘Change storage plan’.
Choose a plan
To start the back up now
Choose Back Up Now from the screen below.