Hello!
I am a moodle administrator with over 8 years of experience installing, managing, upgrading and troubleshooting moodle systems. I have upgraded more than 100 moodle sites. I can upgrade your site from version 3.3 to 3.6.2+ within a couple of hours. I will take full site backup before upgrade to make sure your data is safe.
As per my understanding, you have one additional plugin (level up) installed. It is also required to update your theme to a version that is compatible with moodle 3.6.2+. If the theme is not compatible, we can install and configure a compatible theme.
Please message me to have a discussion and I am glad to answer any questions you may have.
Best Regards,
Malaka