LeanLord Full official steps are listed at https://docs.osticket.com/en/latest/Getting%20Started/Upgrade%20and%20Migration.html , but don't be put off by the length of the document - it's a really simple process that boils down to just a few steps.
- back up your database (don't skip this part!) just in case you need to go back
- put osTicket into offline mode at Admin -> Settings -> System
- upload the 1.12 files in the extracted "upload" folder to your server, overwriting the existing installation
- log in as an admin and follow the prompts to complete the database upgrade
- go back into Admin -> Settings -> System and put osTicket back into online mode
Step 1 (backing up the database) is important, as if you do decide you need to go back for whatever reason, you'll need to restore the 1.10 database - you can't just replace the web server files like you do when upgrading.
Step 2 just stops osTicket from accepting new emails or allowing customers to update anything, ensuring that the upgrade isn't interrupted by somebody replying to a ticket. All emails will be pulled in at step 5 when the system is back online.
Steps 3 and 4 are pretty much all that's involved in the actual upgrade - the rest are just preparation steps ?