How do I prevent loosing my contacts information when upgrading to a new IOS version

Hey Rettelon,
I understand that you would like to ensure that you do not lose anything like your contacts during an upgrade. That is something that you can easily do by simply backing up your iPhone to iCloud or iTunes. Take a look at the link below to walk you through how to back up your data with either option.
How to back up your devices using iCloud or iTunes
https://support.apple.com/en-us/HT203977
If you are using iCloud to sync your data, refer the the next link to walk you through how to make copies of your data . This would ensure that you have a safe copy of your contacts on your computer.
Archive or make copies of your iCloud data
https://support.apple.com/en-us/HT204055
Take it easy