Having a full store backup that includes all store files and the database provides you can restore your site to its original state if anything goes wrong.
The Updates page of the X-Cart App Store highlights the necessity of a full store backup before proceeding with the application of the update.
It also allows you to go directly to the Backup Master add-on page in your store Admin area and make a fresh backup there, provided the add-on is installed and enabled.
If the Backup Master add-on is not installed, make a full cart backup using any other applicable tool.
You can find information on how to make backups in X-Cart here.
In addition, you can create a DEV copy of your store BEFORE running an update on your LIVE store and try applying the update there first. Provided the update goes smoothly, and after you have made sure the store’s DEV copy continues working as expected, you can update your LIVE store with no doubts.