Hi. Have you tried this way?
Restore previous and working backup.
Open administration and disable all plugins, applications and themes you have added.
Rename all innodb tables, and use dynamic row format.
Go to client area and download the latest version of the forum.
Send with ftp the files and folders to your space, making sure to overwrite all files and folders. This is a manual update. See this guide to learn more
Open the browser and proceed with upgrade from your-site/admin/upgrade
If you can log into admin when finished, clear all the cache using the support option in the upper right corner