It enables shop owners to backup and update their site in a few clicks and no technical knowledge.
You should never update your online shop right away. The automatic script can fail in some situations, you might not be able to revert to the previous version.
The safest way is to have an exact copy of your shop available, either on your local computer or in another folder of your web server. It should contain all your products, categories, themes, modules, translations, settings, etc.
Make a trial upgrade on that copy of your shop. Once the upgrade is done, browser your front- and back-office thoroughly to make sure that everything is as expected. If not, then the upgrade tool has an issue with your configuration, and you should use the manual upgrade method, which is longer but safer in your situation.
Downloading and installing the 1-Click Upgrade module