All versions alternately do not need to put in Moodle is built quite a powerful system to upgrade and convert the database.
However, some versions to not miss: because the developers reduce the amount of code that needs to support (because the system exists since 2002).
In the transition from 3.0 to 3.5, you must first upgrade to 3.1
Please note that these versions have different system requirements.
For this reason you can not use the auto-update. And in General it is better never to use it, not to be excruciatingly painful.
I'd do it:
- Turned on the maintenance mode
- Make a complete backup, including code, database and Moodledata.
- Replaced the code with the code version 3.1.x, except config.php
- Updated to 3.1
- Checked the integrity of content, settings, and learning history (all should be well, version not much different, but as they say, better safe).
- Prepared a new server running version 3.5 (with 3.6 not in a hurry, it is short-lived, wait for 3.5 to 2020, then skip to 3.9).
- Made the archive of your database and Moodledata
- Launched an archive on the new server.
- Deployed code the latest version from the 3.5 branch
- Moved config.php, adjusting the settings to connect to the database and the path to Moodledata
- Went into Moodle and run the upgrade procedure.
- Check the safety of the materials and assessments
- Make a complete copy
- Turned off the maintenance mode