Beta 2 to Beta 7 upgrade is not easy. Maybe, not feasible as well
But, you can try a few things
- Use composer to go to a higher version. One version at a time till you reach the latest available
ie, 2-3 3-4 4-5 5-6 etc
But, yes. You will need Composer to do that.
Another option is to use a web-based installer called " Pockethold " by a member for this forum
https://discuss.flarum.org/d/5731-pockethold-a-web-based-installer
It would easier for you to install the latest version removing beta 2