Another option, export the current DB out and store it on a remote location (like your desktop computer). Then you can wipe ALL your existing site and remove the existing DB. If on a VPS/dedi then you need to provision it again and start it off from scratch, and if on shared, you need to remove ALL files/folders that are not there by default in the root directory (usually public_html).
Once you do that, set the site up as a new site from scratch, creating a NEW admin user that is not duplicated in the old DB, then import your old DB into a new database (using a different name than you did/are for the new site) and then do a XenForo -> XenForo import from your old DB. That should allow you to keep all your current posts and users (and their associated info that is XF supported).
You will have to start over on your style/design and reinstall any add-ons since the XF -> XF import will not bring those across. You will also lose any data that those add-ons may have had.
It's better than the alternative.