Ashlamashki Step by step details are at https://docs.osticket.com/en/latest/Getting%20Started/Upgrade%20and%20Migration.html , but it boils down to:

• backup everything
• upload the 1.12 files, overwriting the existing 1.10 installation
• log in as an agent, and follow the prompts to upgrade the database

That should be it! Just make sure you take the backup in step 1, as if you do need to go back for any reason restoring a backup is the only way.

Or this:
https://tmib.net/upgrading-osticket-1-10-x-to-current-1-11-0/