From osTicket Wiki

Upgrade and Migration

Before embarking on an upgrade or a migration mission, it is extremely important that you backup your site's database and files. We also recommend that you take the system offline momentarily during the process. While we try to ensure that the upgrade process is straightforward and painless, we can't guarantee it will be the case for every user. For this reason it is crucial that users take precautions in case of any problems. If the thought of upgrading your installation gives you the shake then feel free to contact us for help.

Upgrade

From time to time it will be necessary to upgrade your osTicket installation to the latest version, either to fix bugs or gain new features. Starting with version 1.6, osTicket is a complete rewrite with new database schema and code base making it hard to simply upgrade from previous versions.

Only previous versions from version 1.6 RC1 can be upgraded to the current version.
If your osTicket version is older than 1.6, you need to look into migration instead.

Our objectives is to make upgrading from an earlier release as painless as possible going forward and support migration from "discontinued" versions. we are working with osTicket community on the best way to upgrade or/and import data from previous versions including 3rd party helpdesk systems.

Uploading files

After you have successfully downloaded the osTicket package to your computer you will need to prepare the files to be uploaded to your web server, where the old version of osTicket is running - overwriting the existing files. This can be accomplished by decompressing the download and then using an FTP client to transfer files in upload directory/folder to your server, overwriting existing osTicket files. For user using control panels like CPanel or Plesk, you can utilize the systems file manager to upload the package to your server then simply extract the package while making sure the path hierarchy is maintained.

Make sure you backup your site's database and files
It is recommended that you take the system offline during the upgrade
Maintain the directory hierarchy to make sure files are overwritten
Upload folder contains the osTicket files that need to be uploaded to your web server.
Do not overwrite your osconfig.php file or else you will lose your MySQL admin settings.
Do not upload files in scripts folder. Only useful for remote piping
For versions 1.6 RC1-RC2 Only
Once you've overwritten the files, rename config.php to ostconfig.php (config.php is found in root osTicket directory).

Note:
If you've customized your osTicket installation, you will need to port the changes to the new version following a successful upgrade. Database changes might cause conflicts.

Running upgrade script

osTicket ships with web-based upgrade wizard to help guide you through the upgrade process. While the wizard provides step by step guide it is important and helpful to have general knowledge about Web servers, PHP and MySQL. Any errors at this stage, although unexpected, are fatal and might require restoring previous version.

To run the upgrade script, point your web browser at http://www.yourdomain.com/osticket/setup/upgrade.php, replacing www.yourdomain.com/osticket/ with the correct URI to your own osTicket installation. When prompted login as admin - the script requires admin level privileges - and follow the instructions.

Post upgrade testing

Once the upgrade has completed, browse to the staff control panel (scp) and check basics such as viewing and responding to test tickets to ensure things still work as expected. After verifying that the upgrade completed correctly do the following;

Enable the helpdesk
Delete setup directory
Explore any new features - see RELEASE NOTES
Take a minute to send us feedback

Migration

We plan on supporting data migration from previous "discontinued" versions of osTicket as well as 3rd party help desks in the near future. Please check the forums for up to date discussions on the subject.