basically you need:
PHP 7.2
pay attention to all php.ini configuration requirements reported by Xibo
Delete the 1.8.11 files, keeping only the ‘web/settings.php’ file (that is your database connection)
Paste the new CMS V2.3 files into the old CMS files folder
Configure the folder ‘vendor/bin’ according to the topic below:
Open CMD in administrator mode, and run the command:
'php vendor/bin/phinx migrate -c phinx.php'
You have migrated to version 2.3, now do the same process, updating the files to version CMS 3.0.3
Delete the files keeping the web/settings.php file
Configure the ‘vendor/bin’ folder (again)
Run the command in CMD in administrator mode:
'php vendor/bin/phinx migrate -c phinx.php'
And that’s it, theoretically it should work fine
Ah important detail!
It may be that some pages do not load correctly, so try increasing the ‘Maximum Query String (Bytes)’ to 8192 in your website server configuration file (web.config or .htaccess, or similar)
Here is the Xibo upgrade tutorial too:
Let me know if it worked!
Hope this helps